Vox Charta » Cosmology and Extragalactic

A comparison of galaxy peculiar velocities field with the PSCz gravity field– A hyper-parameter method

astro-ph — Tue, 22 May 2012 00:55:25 +0000

We constructed a hyper-parameter statistical method to quantify the difference between predicted velocities derived from the observed galaxy distribution in the IRAS-PSCz redshift survey and peculiar velocities measured using different distance indicators. In our analysis we find that the model-data comparison becomes unreliable beyond 70 Mpc/h because of the inadequate sampling of prominent, distant superclusters like the Shapley Concentration by IRAS galaxies. On the other hand, the analysis of the velocity residuals show that the PSCz gravity field provides an adequate model to the local, <= 70 Mpc/h, peculiar velocity field. The hyper-parameter combination of ENEAR, SN, A1SN and SFI++ catalogues constrains the amplitude of the linear flow to \beta=0.53 \pm 0.01. For an rms density fluctuations in the PSCz galaxy number density \sigma_8^{\rm gal}=0.42\pm0.03, we obtain an estimate of the growth rate of density fluctuations $f\sigma_{8}(z\sim0) = 0.42 \pm 0.03$, which is in excellent agreement with independent estimates based on different techniques.

The darkness that shaped the void: dark energy and cosmic voids

astro-ph — Tue, 22 May 2012 00:55:07 +0000

Aims: We assess the sensitivity of void shapes to the nature of dark energy that was pointed out in recent studies. We investigate whether or not void shapes are useable as an observational probe in galaxy redshift surveys. We focus on the evolution of the mean void ellipticity and its underlying physical cause. Methods: We analyse the morphological properties of voids in five sets of cosmological N-body simulations, each with a different nature of dark energy. Comparing voids in the dark matter distribution to those in the halo population, we address the question of whether galaxy redshift surveys yield sufficiently accurate void morphologies. Voids are identified using the parameter free Watershed Void Finder. The effect of redshift distortions is investigated as well. Results: We confirm the statistically significant sensitivity of voids in the dark matter distribution. We identify the level of clustering as measured by \sigma_8(z) as the main cause of differences in mean void shape . We find that in the halo and/or galaxy distribution it is practically unfeasible to distinguish at a statistically significant level between the various cosmologies due to the sparsity and spatial bias of the sample.

The optically unbiased GRB host (TOUGH) survey. VI. Radio observations at z<1 and consistency with typical star-forming galaxies

astro-ph — Tue, 22 May 2012 00:54:52 +0000

We present late-time Hubble Space Telescope imaging of the fields of six Swift GRBs lying at 5.090% confidence. Although it is not yet possible to make stronger statements, in the future, with larger samples and a fuller understanding of the conditions required for GRB production, studies like this hold great potential for probing the nature of star formation, the shape of the galaxy luminosity function, and the supply of ionizing photons in the early universe.

How covariant is the galaxy luminosity function?

astro-ph — Tue, 22 May 2012 00:54:39 +0000

We investigate the error properties of certain galaxy luminosity function (GLF) estimators. Using a cluster expansion of the density field, we show how, for both volume and flux limited samples, the GLF estimates are covariant. The covariance matrix can be decomposed into three pieces: a diagonal term arising from Poisson noise; a sample variance term arising from large-scale structure in the survey volume; an occupancy covariance term arising due to galaxies of different luminosities inhabiting the same cluster. To evaluate the theory one needs: the mass function and bias of clusters, and the conditional luminosity function (CLF). We use a semi-analytic model (SAM) galaxy catalogue from the Millennium run N-body simulation and the CLF of Yang et al. (2003) to explore these effects. The GLF estimates from the SAM and the CLF qualitatively reproduce results from the 2dFGRS. We also measure the luminosity dependence of clustering in the SAM and find reasonable agreement with 2dFGRS results for bright galaxies. However, for fainter galaxies, L

Self-accelerating Massive Gravity: Exact solutions for any isotropic matter distribution [Cross-Listing]

astro-ph — Tue, 22 May 2012 00:54:28 +0000

We present an exact solution to the equations of massive gravity that display cosmological constant-like behavior for any spherically symmetric distribution of matter, including arbitrary time dependence. On this solution, the new degrees of freedom from the massive graviton generate a cosmological constant-like contribution to stress-energy that does not interact directly with other matter sources. When the effective cosmological constant contribution dominates over other sources of stress energy the cosmological expansion self-accelerates, even when no other dark-energy-like ingredients are present. The new degrees of freedom introduced by giving the graviton the mass do not respond to arbitrarily large radial or homogeneous perturbations from other matter fields on this solution. We comment on possible implications of this result.

Physical properties of dense molecular gas in centres of Seyfert galaxies

astro-ph — Tue, 22 May 2012 00:54:11 +0000

We present new ~1″ resolution data of the dense molecular gas in the central 50-100 pc of four nearby Seyfert galaxies. PdBI observations of HCN and, in 2 of the 4 sources, simultaneously HCO+ allow us to carefully constrain the dynamical state of the dense gas surrounding the AGN. Analysis of the kinematics shows large line widths of 100-200 km/s FWHM that can only partially arise from beam smearing of the velocity gradient. The observed morphological and kinematic parameters (dimensions, major axis position angle, red and blue channel separation, and integrated line width) are well reproduced by a thick disk, where the emitting dense gas has a large intrinsic dispersion (20-40 km/s), implying that it exists at significant scale heights (25-30% of the disk radius). To put the observed kinematics in the context of the starburst and AGN evolution, we estimate the Toomre Q parameter. We find this is always greater than the critical value, i.e. Q is above the limit such that the gas is stable against rapid star formation. This is supported by the lack of direct evidence, in these 4 Seyfert galaxies, for on-going star formation close around the AGN. Instead, any current star formation tends to be located in a circumnuclear ring. We conclude that the physical conditions are indeed not suited to star formation within the central ~100 pc.

The Correlated Formation Histories of Massive Galaxies and Their Dark Matter Halos

astro-ph — Tue, 22 May 2012 00:53:48 +0000

Using observations in the COSMOS field, we report an intriguing correlation between the star formation activity of massive (~10^{11.4}\msol) central galaxies, their stellar masses, and the large-scale (~10 Mpc) environments of their group-mass (~10^{13.6}\msol) dark matter halos. Probing the redshift range z=[0.2,1.0], our measurements come from two independent sources: an X-ray detected group catalog and constraints on the stellar-to-halo mass relation derived from a combination of clustering and weak lensing statistics. At z=1, we find that the stellar mass in star-forming centrals is a factor of two less than in passive centrals at the same halo mass. This implies that the presence or lack of star formation in group-scale centrals cannot be a stochastic process. By z=0, the offset reverses, probably as a result of the different growth rates of these objects. A similar but weaker trend is observed when dividing the sample by morphology rather than star formation. Remarkably, we find that star-forming centrals at z~1 live in groups that are significantly more clustered on 10 Mpc scales than similar mass groups hosting passive centrals. We discuss this signal in the context of halo assembly and recent simulations, suggesting that star-forming centrals prefer halos with higher angular momentum and/or formation histories with more recent growth; such halos are known to evolve in denser large-scale environments. If confirmed, this would be evidence of an early established link between the assembly history of halos on large scales and the future properties of the galaxies that form inside them.

X-ray variability of 104 active galactic nuclei. XMM-Newton power-spectrum density profiles

astro-ph — Tue, 22 May 2012 00:53:36 +0000

AGN, powered by accretion onto SMBHs, are thought to be scaled up versions of Galactic black hole X-ray binaries (BH-XRBs). In the past few years evidence of such correspondence include similarities in the broadband shape of the X-ray variability power spectra, with characteristic bend times-scales scaling with mass. We have performed a uniform analysis of the power spectrum densities (PSDs) of 104 nearby (z<0.4) AGN using 209 XMM-Newton/pn observations. The PSDs have been estimated in three energy bands: 0.2-10, 0.2-2, and 2-10 keV. The sample comprises 61 Type-1 AGN, 21 Type-2 AGN, 15 NLSy1, and 7 BLLACS. We have fitted each PSD to two models: (1) a single power-law model and (2) a bending power-law model. Among the entire sample, 72% show significant variability in at least one of the three bands tested. A high percentage of low-luminosity AGN do not show any significant variability. The PSD of the majority of the variable AGN was well described by a simple power-law with a mean index of 2. In 15 sources we found that the bending power law model was preferred with a mean slope of 3 and a mean bend frequency of 2.E-04 Hz. Only KUG1031+398 (REJ1034+396) shows evidence for quasi-periodic oscillations. The `fundamental plane' relating variability timescale, black hole mass, and luminosity is demonstrated using the new X-ray timing results presented here together with a compilation of the previously detected timescales from the literature. Both quantitative (i.e. scaling with BH mass) and qualitative (overall PSD shapes) found in this sample of AGN are in agreement with the expectations for the SMBHs and BH-XRBs being the same phenomenon scaled-up with the size of the BH. The steep PSD slopes above the high frequency bend bear a closer resemblance to those of the `soft/thermal dominated' BH-XRB states than other states.

Galaxies in X-ray Groups II: A Weak Lensing Study of Halo Centering

astro-ph — Tue, 22 May 2012 00:53:20 +0000

Locating the centers of dark matter halos is critical for understanding the mass profiles of halos as well as the formation and evolution of the massive galaxies that they host. The task is observationally challenging because we cannot observe halos directly, and tracers such as bright galaxies or X-ray emission from hot plasma are imperfect. In this paper we quantify the consequences of miscentering on the weak lensing signal from a sample of 129 X-ray selected galaxy groups in the COSMOS field with redshifts 0

Discovery of bright z ~ 7 galaxies in the UltraVISTA survey

astro-ph — Tue, 22 May 2012 00:52:49 +0000

We have exploited the new, deep, near-infrared UltraVISTA imaging of the COSMOS field, in tandem with deep optical and mid-infrared imaging, to conduct a new search for luminous galaxies at redshifts z ~ 7. The unique multi-wavelength dataset provided by VISTA, CFHT, Subaru, HST and Spitzer over a common area of 1 deg^2 has allowed us to select galaxy candidates at z > 6.5 by searching first for Y+J-detected ( 6.5 which we present in this paper. The first four of these appear to be robust galaxies at z > 6.5, and fitting to their stacked SED yields z = 6.98+-0.05 with a stellar mass M* = 5×10^9 Msun, and rest-frame UV spectral slope beta = -2.0+-0.2. The next three are also good candidates for z > 6.5 galaxies, but the possibility that they are low-redshift galaxies or dwarf stars cannot be excluded. Our final subset of three additional candidates is afflicted not only by potential dwarf-star contamination, but also contains objects likely to lie at redshifts just below z = 6.5. We show that the three even-brighter z > 7 galaxy candidates reported in the COSMOS field by Capak et al. (2011) in fact all lie at z ~ 1.5-3.5. Consequently the new z ~ 7 galaxies reported here are the first credible z ~ 7 Lyman-break galaxies discovered in the COSMOS field and, as the most UV-luminous discovered to date at these redshifts, are prime targets for deep follow-up spectroscopy. We explore their physical properties, and briefly consider the implications of their inferred number density for the form of the galaxy luminosity function at z = 7.

An Oxford SWIFT Integral Field Spectroscopy study of 14 early-type galaxies in the Coma cluster

astro-ph — Tue, 22 May 2012 00:51:23 +0000

As a demonstration of the capabilities of the new Oxford SWIFT integral field spectrograph, we present first observations for a set of 14 early-type galaxies in the core of the Coma cluster. Our data consist of I- and z-band spatially resolved spectroscopy obtained with the Oxford SWIFT spectrograph, combined with r-band photometry from the SDSS archive for 14 early- type galaxies. We derive spatially resolved kinematics for all objects from observations of the calcium triplet absorption features at \sim 8500 {AA} . Using this kinematic information we classify galaxies as either Fast Rotators or Slow Rotators. We compare the fraction of fast and slow rotators in our sample, representing the densest environment in the nearby Universe, to results from the ATLAS3D survey, finding the slow rotator fraction is \sim 50 per cent larger in the core of the Coma cluster than in the Virgo cluster or field, a 1.2 {\sigma} increase given our selection criteria. Comparing our sample to the Virgo cluster core only (which is 24 times less dense than the Coma core) we find no evidence of an increase in the slow rotator fraction. Combining measurements of the effective velocity dispersion {\sigma_e} with the photometric data we determine the Fundamental Plane for our sample of galaxies. We find the use of the average velocity dispersion within 1 effective radius, {\sigma_e}, reduces the residuals by 13 per cent with respect to comparable studies using central velocity dispersions, consistent with other recent integral field Fundamental Plane determinations.

The universal density profile of the central region of dark matter haloes

astro-ph — Tue, 22 May 2012 00:50:11 +0000

We consider the density profile of the central region of dark matter haloes. It turns out that under very general conditions the profile is universal: it depends almost not at all on the properties of the initial perturbation and is very akin, but not identical, to the Einasto profile. We estimate the size of the ‘central core’ of the distribution, i.e., the extent of the very central region with a respectively gentle profile, and show that the cusp formation is unlikely, even if the dark matter is cold. We also indicate that the density profile of the outer part ($r>0.5 R_{vir}$) of the haloes significantly depends on the initial conditions and should not be universal, in contrast to the central area. All these results can be useful both to indirect search of the dark matter and to N-body simulations of the structure formation.

Systematic differences in simple stellar population model results: Application to the M31 globular-like cluster system

astro-ph — Tue, 22 May 2012 00:49:34 +0000

Simple stellar population (SSP) synthesis models are useful tools for studying the nature of unresolved star clusters in external galaxies. However, the plethora of currently available SSP models gives rise to significant and poorly documented systematic differences. Here we consider the outputs of the commonly used Bruzual & Charlot and GALEV models, as well as a recently updated SSP model suite which attempts to include the contributions of binary merger products in the form of blue straggler stars (BS-SSP). We rederive the ages, metallicities, extinction values and masses of 445 previously observed globular-like clusters in M31 based on chi-square minimisation of their spectral energy distributions with respect to these three different SSP models and adopting a Chabrier-like stellar initial mass function. A comparison between our new results and previous estimates of the same parameters shows that the Bruzual & Charlot models yield the youngest ages and lowest masses, while adoption of the BS-SSP models results in the oldest ages and highest mass estimates. Similarly, the GALEV SSP models produce the lowest metallicities, with the highest values resulting from the BS-SSP model suite. These trends are caused by intrinsic differences associated with the models, and are not significantly affected by the well-known age-metallicity degeneracy. Finally, we note that the mass function of the massive M31 star clusters is similar to that of the Milky Way’s globular clusters, which implies that the two star cluster systems likely formed under similar environmental conditions.

Monster black holes

astro-ph — Tue, 22 May 2012 00:48:37 +0000

A combination of ground-based and spacecraft observations has uncovered two black holes of 10 billion solar masses in the nearby Universe. The finding sheds light on how these cosmic monsters co-evolve with galaxies.

Towards p-Adic Matter in the Universe [Cross-Listing]

astro-ph — Tue, 22 May 2012 00:47:58 +0000

Starting from p-adic string theory with tachyons, we introduce a new kind of non-tachyonic matter which may play an important role in evolution of the Universe. This matter retains nonlocal and nonlinear p-adic string dynamics, but does not suffer of negative square mass. In space-time dimensions D = 2 + 4k, what includes D = 6, 10, …, 26, the kinetic energy term also maintains correct sign. In these spaces this p-adic matter provides negative cosmological constant and time-dependent scalar field solution with negative potential. Their possible cosmological role is discussed. We have also connected non-locality with string world-sheet in effective Lagrangian for p-adic string.

CfA4: Light Curves for 94 Type Ia Supernovae

astro-ph — Tue, 22 May 2012 00:45:42 +0000

We present multi-band optical photometry of 94 spectroscopically-confirmed Type Ia supernovae (SN Ia) in the redshift range 0.0055 to 0.073, obtained between 2006 and 2011. There are a total of 5522 light curve points. We show that our natural system SN photometry has a precision of roughly 0.03 mag or better in BVr’i', 0.06 mag in u’, and 0.07 mag in U for points brighter than 17.5 mag and estimate that it has a systematic uncertainty of 0.014, 0.010, 0.012, 0.014, 0.046, and 0.073 mag in BVr’i'u’U, respectively. Comparisons of our standard system photometry with published SN Ia light curves and comparison stars reveal mean agreement across samples in the range of ~0.00-0.03 mag. We discuss the recent measurements of our telescope-plus-detector throughput by direct monochromatic illumination by Cramer et al (in prep.). This technique measures the whole optical path through the telescope, auxiliary optics, filters, and detector under the same conditions used to make SN measurements. Extremely well-characterized natural-system passbands (both in wavelength and over time) are crucial for the next generation of SN Ia photometry to reach the 0.01 mag accuracy level. The current sample of low-z SN Ia is now sufficiently large to remove most of the statistical sampling error from the dark energy error budget. But pursuing the dark-energy systematic errors by determining highly-accurate detector passbands, combining optical and near-infrared (NIR) photometry and spectra, using the nearby sample to illuminate the population properties of SN Ia, and measuring the local departures from the Hubble flow will benefit from larger, carefully measured nearby samples.

IR-derived covering factors for a large sample of quasars from WISE-UKIDSS-SDSS

astro-ph — Tue, 22 May 2012 00:44:12 +0000

We investigate the range of covering factors (determined from the ratio of IR to UV/optical luminosity) seen in luminous quasars using a combination of data from the WISE, UKIDSS and SDSS surveys. Accretion disk (UV/optical) and obscuring dust (IR) luminosities are measured via the use of a simple three component SED model. We use these estimates to investigate the distribution of covering factors and its relationship to both accretion luminosity and IR SED shape. The distribution of covering factors (f_C) is observed to be log-normal, with a bias-corrected mean of =-0.48 and standard deviation of 0.19. The fraction of IR luminosity emitted in the near-IR (1–5 micron) is found to be high (~40 per cent), and dependant on covering factor.

Comparison of star formation rates from Halpha and infrared luminosities as seen by Herschel

astro-ph — Tue, 22 May 2012 00:43:27 +0000

We empirically test the relation between the SFR(LIR) derived from the infrared luminosity, LIR, and the SFR(Ha) derived from the Ha emission line luminosity using simple conversion relations. We use a sample of 474 galaxies at z = 0.06 – 0.46 with both Ha detection (from 20k zCOSMOS survey) and new far-IR Herschel data (100 and 160 {\mu}m). We derive SFR(Ha) from the Ha extinction corrected emission line luminosity. We find a very clear trend between E(B – V) and LIR that allows to estimate extinction values for each galaxy even if the Ha emission line measurement is not reliable. We calculate the LIR by integrating from 8 up to 1000 {\mu}m the SED that is best fitting our data. We compare SFR(Ha) with the SFR(LIR). We find a very good agreement between the two SFR estimates, with a slope of m = 1.01 \pm 0.03 in the SFR(LIR) vs SFR(Ha) diagram, a normalization constant of a = -0.08 \pm 0.03 and a dispersion of sigma = 0.28 dex.We study the effect of some intrinsic properties of the galaxies in the SFR(LIR)-SFR(Ha) relation, such as the redshift, the mass, the SSFR or the metallicity. The metallicity is the parameter that affects most the SFR comparison. The mean ratio of the two SFR estimators log[SFR(LIR)/SFR(Ha)] varies by approx. 0.6 dex from metal-poor to metal-rich galaxies (8.1 < log(O/H) + 12 < 9.2). This effect is consistent with the prediction of a theoretical model for the dust evolution in spiral galaxies. Considering different morphological types, we find a very good agreement between the two SFR indicators for the Sa, Sb and Sc morphologically classified galaxies, both in slope and normalization. For the Sd, irregular sample (Sd/Irr), the formal best-fit slope becomes much steeper (m = 1.62 \pm 0.43), but it is still consistent with 1 at the 1.5 sigma level, because of the reduced statistics of this sub-sample.

The structure of phase space close to fixed points in a 4D symplectic map [Cross-Listing]

astro-ph — Tue, 22 May 2012 00:43:15 +0000

We study the dynamics in the neighborhood of fixed points in a 4D symplectic map by means of the color and rotation method. We compare the results with the corresponding cases encountered in galactic type potentials and we find that they are in good agreement. The fact that the 4D phase space close to fixed points is similar to the 4D representations of the surfaces of section close to periodic orbits, indicates an archetypical 4D pattern for each kind of (in)stability, not only in 3D autonomous Hamiltonian systems with galactic type potentials but for a larger class of dynamical systems. This pattern is successfully visualized with the method we use in the paper.

Remarks on the Cosmological Constant

astro-ph — Tue, 22 May 2012 00:43:01 +0000

Assuming only Einstein’s general theory of relativity, it is shown that the present observational data make it inevitable that (i) the cosmological constant Lambda must be non-zero and (ii) must be positive and less or of order $10^{-124}$ in Planck units. The co-moving radius R(t_0) of the spherical visible universe which is bounded by the surface of the last scatter, and the mass-energy M(t_0) contained therein lead to an outwardly accelerating cosmological expansion corresponding to that observed. The dark energy does not require a modification of general relativity but follows from it.

Effect of metallicity on the gravitational-wave signal from the cosmological population of compact binary coalescences

astro-ph — Tue, 22 May 2012 00:42:04 +0000

Recent studies on stellar evolution have shown that the properties of compact objects strongly depend on metallicity of the environment in which they were formed. In this work, we study how the metallicity of the stellar population can affect unresolved gravitational waves background from extragalactic compact binaries. We obtain a suit of models of compact binaries using population synthesis code and estimate the gravitational wave background they produce. Our results show a double peaked structure for all considered models with the first peak between 30-100Hz caused by the binary black holes population and the second between 500-1000Hz corresponding to the double neutron stars population. We discuss the detectability of gravitational waves background with second (Advanced LIGO, Advanced Virgo) and third (Einstein Telescope) generation detectors.

Cosmic Flows surveys and CLUES simulations

astro-ph — Tue, 22 May 2012 00:41:47 +0000

Cosmic Flows is a program to determine galaxy distances for 30,000 galaxies with systematic errors below 2%, almost ten times the number currently known and a five-fold improvement in systematics. The resultant velocity field will provide input for constrained local universe simulations: CLUES (www.clues-project.org). The observed and the simulated universe are then comparatively studied. This synergy of observations and theory distinguishes the program, and should lead to fundamental discoveries regarding the sources of deviations from the expansion of the universe. Specifically, the program should give a definitive answer to one of the most outstanding unsolved problem in cosmology: the cause of the motion of 630 km/s of our Galaxy manifested in the microwave background dipole. This paper presents current results with particular emphasis on the “great attractor” reconstruction.

Fermi Gamma Ray Line at 130 GeV from Axion-Mediated Dark Matter [Cross-Listing]

astro-ph — Tue, 22 May 2012 00:41:02 +0000

We consider a singlet fermion dark matter with PQ symmetry. A singlet complex scalar is introduced to mediate between dark matter and the SM through Higgs portal interaction and electroweak PQ anomalies. We show that dark matter annihilation with axion mediation can explain a monochromatic photon line of the Fermi LAT data at 130 GeV by anomaly interactions while the annihilation cross section with Higgs portal interaction is p-wave suppressed. We discuss the interplay between direct detection of the fermion dark matter and the collider search of Higgs-like scalars. We also present a ultra-violet completion of the dark matter model into the NMSSM with PQ symmetry.

Testing some f(R,T) gravity models from energy conditions [Cross-Listing]

astro-ph — Tue, 22 May 2012 00:40:50 +0000

We consider f(R; T) theory of gravity, where R is the curvature scalar and T the trace of the energy momentum tensor. Attention is attached to the special case, f(R; T) = R + 2f(T) as a f(T) correction to the Einstein-Hilbert term. Two expressions are assumed for the function f(T), $\frac{a_1T^n+b_1}{a_2T^n+b_2}$ and $a_3ln^q(b_3T^m)$, where $a1$, $a2$, $b1$, $b2$, $n$, $a3$, $b3$, $q$ and $m$ are input parameters. We observe that by adjusting suitably these input parameters, energy conditions are satis?fied and viable f(R; T) models corresponding to the two assumptions of f(T) may be obtained.

A combined measurement of cosmic growth and expansion from clusters of galaxies, the CMB and galaxy clustering

astro-ph — Tue, 22 May 2012 00:40:37 +0000

Combining galaxy cluster data from the ROSAT All-Sky Survey and the Chandra X-ray Observatory, cosmic microwave background data from the Wilkinson Microwave Anisotropy Probe, and galaxy clustering data from the WiggleZ Dark Energy Survey, the 6-degree Field Galaxy Survey and the Sloan Digital Sky Survey III, we test for consistency the cosmic growth of structure predicted by General Relativity (GR) and the cosmic expansion history predicted by the cosmological constant plus cold dark matter paradigm (LCDM). The combination of these three independent, well studied measurements of the evolution of the mean energy density and its fluctuations is able to break strong degeneracies between model parameters. We model the key properties of cosmic growth with the normalization of the matter power spectrum, sigma_8, and the cosmic growth index, gamma, and those of cosmic expansion with the mean matter density, Omega_m, the Hubble constant, H_0, and a kinematical parameter equivalent to that for the dark energy equation of state, w. To further tighten constraints on the expansion parameters, we also include supernova, baryon acoustic oscillation and Cepheid variable data. For a spatially flat geometry, w=-1, and allowing for systematic uncertainties, we obtain sigma_8=0.787+-0.019 and gamma=0.576+0.058-0.059 (at the 68.3 per cent confidence level). Allowing w to vary, we find Omega_m=0.256+-0.011, H_0=71.5+-1.3 km s^-1 Mpc^-1 and w=-0.968+-0.049 for the expansion parameters, and sigma_8=0.783+0.020-0.019 and gamma=0.546+0.071-0.072 for the growth parameters. These results are in excellent agreement with GR+LCDM (gamma~0.55; w=-1) and represent the tightest and most robust simultaneous constraint on cosmic growth and expansion to date.

Is the transition redshift a new cosmological number?

astro-ph — Tue, 22 May 2012 00:40:21 +0000

Observations from Supernovae Type Ia (SNe Ia) provided strong evidence for an expanding accelerating Universe at intermediate redshifts. This means that the Universe underwent a dynamic phase transition from deceleration to acceleration at a transition redshift $z_t$ of the order unity whose value in principle depends on the cosmology as well as on the assumed gravitational theory. Since cosmological accelerating models endowed with a transition redshift are extremely degenerated, in principle, it is interesting to know whether the value of $z_t$ itself can be observationally used as a new cosmic discriminator. After a brief discussion of the potential dynamic role played by the transition redshift, it is argued that future observations combining SNe Ia, the line-of-sight (or “radial”) baryon acoustic oscillations, the differential age of galaxies, as well as the redshift drift of the spectral lines may tightly constrain $z_t$, thereby helping to narrow the parameter space for the most realistic models describing the accelerating Universe.

Evolution of the baryon fraction in the Local Group: accretion versus feedback at low and high z

astro-ph — Tue, 22 May 2012 00:39:42 +0000

Using hydrodynamical zoom simulations in the standard LCDM cosmology, we investigate the evolution of the distribution of baryons (gas and stars) in a local group-type universe. First, with standard star formation and supernova feedback prescriptions, we find that the mean baryonic fraction value estimated at the virial radius of the two main central objects (i.e. the Milky Way and Andromeda) is decreasing over time, and is 10-15% lower than the universal value, 0.166, at z=0. This decrease is mainly due to the fact that the amount of accretion of dissipative gas onto the halo, especially at low redshift, is in general much lower than that of the dissipationless dark matter. Indeed, a significant part of the baryons does not collapse onto the haloes and remains in their outskirts, mainly in the form of warm-hot intergalactic medium (WHIM). Moreover, during the formation of each object, some dark matter and baryons are also be expelled through merger events via tidal disruption. In contrast to baryons, expelled dark matter can be more efficiently re-accreted onto the halo, enhancing both the reduction of fb inside Rv, and the increase of the mass of WHIM outside Rv. Varying the efficiency of supernovae feedback at low redshift does not seem to significantly affect these trends. Alternatively, when a significant fraction of the initial gas in the main objects is released at high redshifts by more powerful sources of feedback, such as AGN from intermediate mass black holes in lower mass galaxies, the baryonic fraction at the virial radius can have a lower value (fb~0.12) at low redshift. Hence physical mechanisms able to slow down the accretion of gas at high redshifts will have a stronger impact on the deficit of baryons in the mass budget of Milky Way type-galaxies at present times than those that expel the gas in the longer, late phases of galaxy formation.

X-Ray And Optical Flux Ratio Anomalies In Quadruply Lensed Quasars. II. Mapping the Dark Matter Content in Elliptical Galaxies [Replacement]

astro-ph — Tue, 22 May 2012 00:38:41 +0000

We present a microlensing analysis of 61 Chandra observations of 14 quadruply lensed quasars. X-ray flux measurements of the individual quasar images give a clean determination of the microlensing effects in the lensing galaxy and thus offer a direct assessment of the local fraction of stellar matter making up the total integrated mass along the lines of sight through the lensing galaxy. A Bayesian analysis of the ensemble of lensing galaxies gives a most likely local stellar fraction of 7%, with the other 93% in a smooth, dark matter component, at an average impact parameter R_c of 6.6 kpc from the center of the lensing galaxy. We divide the systems into smaller ensembles based on R_c and find that the most likely local stellar fraction varies qualitatively and quantitatively as expected, decreasing as a function of R_c.

A new signature of primordial non-Gaussianities from the abundance of galaxy clusters [Replacement]

astro-ph — Tue, 22 May 2012 00:38:30 +0000

The evolution with time of the abundance of galaxy clusters is very sensitive to the statistical properties of the primordial density perturbations. It can thus be used to probe small deviations from Gaussianity in the initial conditions. The characterization of such deviations would help distinguish between different inflationary scenarios, and provide us with information on physical processes which took place in the early Universe. We have found that when the information contained in the galaxy cluster counts is used to reconstruct the dark energy equation of state as a function of redshift, assuming erroneously that no primordial non-Gaussianities exist, an apparent evolution with time in the effective dark energy equation of state arises,characterized by the appearance of a clear discontinuity.

Modified Newtonian Dynamics (MOND): Observational Phenomenology and Relativistic Extensions [Replacement]

astro-ph — Tue, 22 May 2012 00:38:08 +0000

A wealth of astronomical data indicate the presence of mass discrepancies in the Universe. The motions observed in a variety of classes of extragalactic systems exceed what can be explained by the mass visible in stars and gas. Either (i) there is a vast amount of unseen mass in some novel form – dark matter – or (ii) the data indicate a breakdown of our understanding of dynamics on the relevant scales, or (iii) both. Here, we first review a few outstanding challenges for the dark matter interpretation of mass discrepancies in galaxies, purely based on observations and independently of any alternative theoretical framework. We then show that many of these puzzling observations are predicted by one single relation – Milgrom’s law – involving an acceleration constant (or a characteristic surface density) of the order of the square-root of the cosmological constant in natural units. This relation can at present most easily be interpreted as the effect of a single universal force law resulting from a modification of Newtonian dynamics (MOND) on galactic scales. We exhaustively review the current observational successes and problems of this alternative paradigm at all astrophysical scales, and summarize the various theoretical attempts (TeVeS, GEA, BIMOND, and others) made to effectively embed this modification of Newtonian dynamics within a relativistic theory of gravity.

Star formation in LINER host galaxies at z~0.3 [Replacement]

astro-ph — Tue, 22 May 2012 00:36:21 +0000

We present the results of a Herschel-PACS study of a sample of 97 LINERs at redshift z\sim 0.3 selected from the zCOSMOS survey. Of these sources, 34 are detected in a least one PACS band, enabling reliable estimates of the far-infrared L(FIR) luminosities, and a comparison to the FIR luminosities of local LINERs. Many of our PACS-detected LINERs are also UV sources detected by Galex. Assuming that the FIR is produced in young dusty star-forming regions, the typical star-formation rates (SFRs) for the host galaxies in our sample is \sim 10 M_Sun yr-1, 1-2 orders of magnitude larger than in many local LINERs. Given stellar masses inferred from optical/NIR photometry of the (unobscured) evolved stellar populations, we find that the entire sample lies close to the star-forming “main sequence” for galaxies at redshift 0.3. For young star-forming regions, the H\alpha- and UV-based estimates of the SFRs are much smaller than the FIR-based estimates, by factors \sim 30, even assuming that all of the H\alpha\ emission is produced by O-star ionization rather than by the AGNs. These discrepancies may be due to large (and uncertain) extinctions towards the young stellar systems. Alternatively, the H\alpha\ and UV emissions could be tracing residual star-formation in an older less obscured population with decaying star formation. We also compare L(SF) and L(AGN) in local LINERs and in our sample and comment on the problematic use of several line diagnostic diagrams in cases similar to the sample under study.

Star formation in the early universe: beyond the tip of the iceberg [Replacement]

astro-ph — Tue, 22 May 2012 00:35:02 +0000

We present late-time Hubble Space Telescope imaging of the fields of six Swift GRBs lying at 5.0

Effective theories of single field inflation when heavy fields matter [Replacement]

astro-ph — Tue, 22 May 2012 00:34:51 +0000

We compute the low energy effective field theory (EFT) expansion for single-field inflationary models that descend from a parent theory containing multiple other scalar fields. By assuming that all other degrees of freedom in the parent theory are sufficiently massive relative to the inflaton, it is possible to derive an EFT valid to arbitrary order in perturbations, provided certain generalized adiabaticity conditions are respected. These conditions permit a consistent low energy EFT description even when the inflaton deviates off its adiabatic minimum along its slowly rolling trajectory. By generalizing the formalism that identifies the adiabatic mode with the Goldstone boson of this spontaneously broken time translational symmetry prior to the integration of the heavy fields, we show that this invariance of the parent theory dictates the entire non-perturbative structure of the descendent EFT. The couplings of this theory can be written entirely in terms of the reduced speed of sound of adiabatic perturbations. The resulting operator expansion is distinguishable from that of other scenarios, such as standard single inflation or DBI inflation. In particular, we re-derive how certain operators can become transiently strongly coupled along the inflaton trajectory, consistent with slow-roll and the validity of the EFT expansion, imprinting features in the primordial power spectrum, and we deduce the relevant cubic operators that imply distinct signatures in the primordial bispectrum which may soon be constrained by observations.

The clustering of galaxies as a function of their photometrically-estimated atomic gas content [Replacement]

astro-ph — Tue, 22 May 2012 00:34:15 +0000

We introduce a new photometric estimator of the HI mass fraction (M_HI/M_*) in local galaxies, which is a linear combination of four parameters: stellar mass, stellar surface mass density, NUV-r colour, and g-i colour gradient. It is calibrated using samples of nearby galaxies (0.025

Probing cluster dynamics in RXCJ1504.1-0248 via radial and two-dimensional gas and galaxy properties [Replacement]

astro-ph — Tue, 22 May 2012 00:32:55 +0000

We studied one of the most X-ray luminous cluster of galaxies in the REFLEX survey, RXC J1504.1-0248 (hereafter R1504; z=0.2153), using XMM-Newton X-ray imaging spectroscopy, VLT/VIMOS optical spectroscopy, and WFI optical imaging. The mass distributions were determined using both the so-called hydrostatic method with X-ray imaging spectroscopy and the dynamical method with optical spectroscopy, respectively, which yield M^{H.E.}_{500}=(5.81+/-0.49)*1.e14Msun and M^{caustic}_{500}=(4.17+/-0.42)*1e14Msun. According to recent calibrations, the richness derived mass estimates closely agree with the hydrostatic and dynamical mass estimates. The line-of-sight velocities of spectroscopic members reveal a group of galaxies with high-velocities (>1000 km/s) at a projected distance of about r^{H.E.}_{500}=(1.18+/-0.03) Mpc south-east of the cluster centroid, which is also indicated in the X-ray two-dimensional (2-D) temperature, density, entropy, and pressure maps. The dynamical mass estimate is 80% of the hydrostatic mass estimate at r^{H.E.}_{500}. It can be partially explained by the ~20% scatter in the 2-D pressure map that can be propagated into the hydrostatic mass estimate. The uncertainty in the dynamical mass estimate caused by the substructure of the high velocity group is ~14%. The dynamical mass estimate using blue members is 1.23 times that using red members. The global properties of R1504 obey the observed scaling relations of nearby clusters, although its stellar-mass fraction is rather low.

Revisit of the Interaction between Holographic Dark Energy and Dark Matter [Replacement]

astro-ph — Tue, 22 May 2012 00:32:33 +0000

In this paper we investigate the possible direct, non-gravitational interaction between holographic dark energy (HDE) and dark matter. Firstly, we start with two simple models with the interaction terms $Q \propto \rho_{dm}$ and $Q \propto \rho_{de}$, and then we move on to the general form $Q \propto \rho_m^\alpha\rho_{de}^\beta$. The cosmological constraints of the models are obtained from the joint analysis of the present Union2.1+BAO+CMB+$H_0$ data. We find that the data slightly favor an energy flow from dark matter to dark energy, although the original HDE model still lies in the 95.4% confidence level (CL) region. For all models we find $c<1$ at the 95.4% CL. We show that compared with the cosmic expansion, the effect of interaction on the evolution of $\rho_{dm}$ and $\rho_{de}$ is smaller, and the relative increment (decrement) amount of the energy in the dark matter component is constrained to be less than 9% (15%) at the 95.4% CL. By introducing the interaction, we find that even when $c<1$ the big rip still can be avoided due to the existence of a de Sitter solution at $z\rightarrow-1$. We show that this solution can not be accomplished in the two simple models, while for the general model such a solution can be achieved with a large $\beta$, and the big rip may be avoided at the 95.4% CL.

Warm Gas in the Virgo Cluster: I. Distribution of Lya Absorbers [Replacement]

astro-ph — Tue, 22 May 2012 00:32:17 +0000

The first systematic study of the warm gas (T=10^4-5 K) distribution across a galaxy cluster is presented using multiple background QSOs to the Virgo Cluster. We detect 25 Lya absorbers (N_HI = 10^13.1-15.4 cm^-2) in the Virgo velocity range toward 9 of 12 QSO sightlines observed with COS, with a cluster impact parameter range of 0.25-1.15 Mpc (0.23-1.05R_vir). Including 18 Lya absorbers previously detected by STIS or GHRS toward 7 of 11 background QSOs in and around the Virgo Cluster, we establish a sample of 43 absorbers towards a total of 23 background probes for studying the incidence of Lya absorbers in and around the Virgo Cluster. With these absorbers, we find: 1) Warm gas is predominantly in the outskirts of the cluster and avoids the X-ray detected hot ICM. Also, Lya absorption strength increases with a cluster impact parameter. 2) Lya absorbing warm gas traces cold HI emitting gas in the substructures of the Virgo Cluster. 3) Including the absorbers associated with the surrounding substructures, the warm gas covering fraction (100% for N_HI > 10^13.1 cm^-2) is in agreement with cosmological simulations. We speculate that the observed warm gas is part of large-scale gas flows feeding the cluster both the ICM and galaxies.

Planck Intermediate Results. IV. The XMM-Newton validation programme for new Planck clusters [Replacement]

astro-ph — Tue, 22 May 2012 00:31:48 +0000

We present the final results from the XMM-Newton validation follow-up of new Planck cluster candidates. We observed 15 new candidates, detected with signal-to-noise ratios between 4.0 and 6.1 in the 15.5-month nominal Planck survey. The candidates were selected using ancillary data flags derived from the ROSAT All Sky Survey (RASS) and Digitized Sky Survey all-sky maps, with the aim of pushing into the low SZ flux, high- z regime and testing RASS flags as indicators of candidate reliability. 14 new clusters were detected by XMM-Newton, 10 single clusters and 2 double systems. Redshifts from X-ray spectroscopy lie in the range 0.2 to 0.9, with six clusters at z>0.5. Estimated M500 ranges from 2.5 X 10^14 to 8 X 10^14 Msun. We discuss our results in the context of the full XMM validation programme, in which 51 new clusters have been detected. This includes 4 double and 2 triple systems, some of which are chance projections on the sky of clusters at different redshifts. Association with a source from the RASS-Bright Source Catalogue is a robust indicator of candidate reliability, whereas association with a source from the RASS-Faint Source Catalogue does not guarantee that the SZ candidate is a bona fide cluster. Most Planck clusters appear in RASS maps, with a significance greater than 2 sigma being a good indication of a real cluster. The full sample indicates a Planck sensitivity threshold of Y500 ~ 4 X 10^-4 arcmin^2, with indication for Malmquist bias in the YX-Y500 relation below this level. The corresponding mass threshold depends on redshift. Systems with M500 > 5 X 10^14 Msun at z>0.5 are easily detectable with Planck. The newly-detected clusters follow the YX-Y500 relation derived from X-ray selected samples, with no indication of evolution. Compared to X-ray selected clusters, the new SZ clusters are underluminous on average for their mass, at all redshifts.

Galaxy mass, cluster-centric distance and secular evolution: their role in the evolution of galaxies in clusters in the last 10 Gyr [Replacement]

astro-ph — Tue, 22 May 2012 00:31:22 +0000

Galaxy mass and environment are known to play a key role in galaxy evolution: looking at galaxy colors at different redshifts, fixed galaxy mass and environment, offers a powerful diagnosis to disentangle the role of each. In this work, we study the simulateneous dependence of the fraction of blue galaxies fblue on secular evolution, environment and galaxy mass with a well-controlled cluster sample. We are thus able to study the evolution and respective role of the cessation of star formation history (SFH) in clusters due to galaxy mass (“mass quenching”) or to environment (“environmental quenching”). We define an homogenous X-ray selected cluster sample (25 clusters with 0 < z < 1 and one cluster at z \sim 2.2), having similar masses and well-defined sizes. Using multicolor photometry and a large spectroscopic sample to calibrate photometric redshifts, we carefully estimate fblue for each cluster at different galaxy mass and cluster-centric distance bins. We then fit with a simple model the dependence of fblue on redshift (z), environment (r/r200) and galaxy mass (M). fblue increases with cluster-centric distance with a slope $1.2^{+0.4}_{-0.3}$, decreases with galaxy mass with a slope $-3.8^{+0.6}_{-0.5}$, and increases with redshift with a slope $3.2^{+0.7}_{-0.5}$. The data also require for the first time a differential evolution with galaxy mass of fblue with redshift, with lower mass galaxies evolving slower by a factor $-4.1^{+1.1}_{-0.9}$. Our study shows that the processes responsible for the cessation of star formation in clusters are effective at all epochs (z<2.2), and more effective in denser environments and for more massive galaxies. We found that the mass and environmental quenchings are separable, that environmental quenching does not change with epoch, and that mass quenching is a dynamical process, i.e. its evolutionary rate is mass-dependent. [Abridged]

Galaxy mass, cluster-centric distance and secular evolution: their role in the evolution of galaxies in clusters in the last 10 Gyr

astro-ph — Mon, 21 May 2012 00:45:48 +0000

Probing ionizing radiation of L<~0.1L* star-forming galaxies at z>~3 with strong lensing

astro-ph — Mon, 21 May 2012 00:44:46 +0000

We show the effectiveness of strong lensing in the characterisation of Lyman continuum emission from faint L~ 3. Past observations of L>~L* galaxies at redshift >~3 have provided upper limits of the average escape fraction of ionising radiation of fesc~5%. Galaxies with relatively high fesc (>10%) seem to be particularly rare at these luminosities, there is therefore the need to explore fainter limits. Before the advent of giant ground based telescopes, one viable way to probe fesc down to 0.05-0.15L* is to exploit strong lensing magnification. This is investigated with Monte Carlo simulations that take into account the current observational capabilities. Adopting a lensing cross-section of 10 arcmin^2 within which the magnification is higher than 1 (achievable with about 4-5 galaxy clusters), with a U-band survey depth of 30(30.5) (AB, 1-sigma), it is possible to constrain fesc for z~3 star-forming galaxies down to 15(10)% at 3-sigma for L<0.15L* luminosities. This is particularly interesting if fesc increases at fainter luminosities, as predicted from various HI reionization scenarios and radiation transfer modelling. Ongoing observational programs on galaxy clusters are discussed and offer positive prospects for the future, even though from space the HST/WFC3 instrument represents the only option we have to investigate details of the spatial distribution of the Lyman continuum emission arising from z~2-4 galaxies.

Search for cold gas in strong MgII absorbers at 0.5
astro-ph — Mon, 21 May 2012 00:44:34 +0000

We report 4 new detections of 21-cm absorption from a systematic search of 21-cm absorption in a sample of 17 strong (Wr(MgII 2796)>1A) intervening MgII absorbers at 0.5

A New Population of High Redshift, Dusty Lyman-Alpha Emitters and Blobs Discovered by WISE

astro-ph — Mon, 21 May 2012 00:44:13 +0000

We report a new technique to select 1.6

On the local dark matter density

astro-ph — Mon, 21 May 2012 00:43:56 +0000

An analysis of the kinematics of 412 stars at 1-4 kpc from the Galactic mid-plane by Moni Bidin et al. (2012) has claimed to derive a local density of dark matter that is an order of magnitude below standard expectations. We show that this result is incorrect and that it arises from the invalid assumption that the mean azimuthal velocity of the stellar tracers is independent of Galactocentric radius at all heights; the correct assumption—that is, the one supported by data—is that the circular speed is independent of radius in the mid-plane. We demonstrate that the assumption of constant mean azimuthal velocity is physically implausible by showing that it requires the circular velocity to drop more steeply than allowed by any plausible mass model, with or without dark matter, at large heights above the mid-plane. Using the correct approximation that the circular velocity curve is flat in the mid-plane, we find that the data imply a local dark-matter density of 0.008 +/- 0.002 Msun/pc^3= 0.3 +/- 0.1 Gev/cm^3, fully consistent with standard estimates of this quantity. This is the most robust direct measurement of the local dark-matter density to date.

Resolved [CII] emission in a lensed quasar at z=4.4

astro-ph — Mon, 21 May 2012 00:43:27 +0000

We present one of the first resolved maps of the [CII] 158 micron line, a powerful tracer of the star forming inter-stellar medium, at high redshift. We use the new IRAM PdBI receivers at 350 GHz to map this line in BRI 0952-0115, the host galaxy of a lensed quasar at z=4.4 previously found to be very bright in [CII] emission. The [CII] emission is clearly resolved and our data allow us to resolve two [CII] lensed images associated with the optical quasar images. We find that the star formation, as traced by [CII], is distributed over a region of ~ 1 kpc in size near the quasar nucleus, and we infer a star formation surface density >150 Msun/yr/kpc^2, similar to that observed in local ULIRGs. We also reveal another [CII] component, extended over ~ 12 kpc, and located at ~ 10 kpc from the quasar. We suggest that this component is a companion disk galaxy, in the process of merging with the quasar host, whose rotation field is distorted by the interaction with the quasar host, and where star formation, although intense, is more diffuse. These observations suggest that galaxy merging at high-z can enhance star formation at the same time in the form of more compact regions, in the vicinity of the accreting black hole, and in more extended star forming galaxies.

The optically unbiased GRB host (TOUGH) survey. V. VLT/X-shooter emission-line redshifts for Swift GRBs at z~2

astro-ph — Mon, 21 May 2012 00:43:14 +0000

We present simultaneous optical and near-infrared (NIR) spectroscopy of 19 Swift GRB host galaxies with VLT/X-shooter with the aim of measuring their redshifts. Galaxies were selected from The Optically Unbiased GRB Host (TOUGH) survey (15 of the 19 galaxies) or because they hosted GRBs without a bright optical afterglow. Here, we provide emission-line redshifts for 13 of the observed galaxies with brightnesses between F606W > 27 mag and R=22.9 mag (median R=24.6 mag). The median redshift is z=2.1 for all, and z=2.3 for the TOUGH hosts. Our new data significantly improve the redshift completeness of the TOUGH survey, which now stands at 77% (53 out of 69 GRBs). They furthermore provide accurate redshifts for eight prototype-dark GRBs (e.g., GRBs 071021 at z=2.452 and 080207 at z=2.086), which are exemplary of GRBs where redshifts are challenging to obtain via afterglow spectroscopy. This establishes X-shooter spectroscopy as an efficient tool for redshift determination of faint, star-forming, high-redshift galaxies such as GRB hosts. It is hence a further step towards removing the bias in GRB samples that is caused by optically-dark events, and provides the basis for a better understanding of the conditions in which GRBs form. The distribution of column densities as measured from X-ray data (N_{H,X}), for example, is closely related to the darkness of the afterglow and skewed towards low N_{H, X} values in samples that are dominated by bursts with bright optical afterglows.

Empirical Constraints of Super-Galactic Winds at z >= 0.5

astro-ph — Mon, 21 May 2012 00:42:06 +0000

(Abridged) Under the hypothesis that MgII absorbers found near the minor axis of a galaxy originate in the cool phase of winds, we carry out a study to constrain the properties of large-scale outflows at redshift z >= 0.5 based on the observed relative motions of individual absorbing clouds with respect to the positions and orientations of the galaxies. We identify in the literature four highly inclined disk galaxies located within 50 kpc and with the minor axis oriented within 45 degrees of a background QSO sightline. Deep HST images of the galaxies are available for accurate morphologies of the galaxies. Echelle spectra of the QSO members are also available in public archives for resolving the velocity field of individual absorption clumps. Three galaxies in our sample are located at rho=8-34 kpc and exhibit strong associated MgII absorption feature with Wr(2796) >= 0.8 {\AA}. One galaxy, located at an impact parameters rho=48 kpc, does not show an associated MgII absorber to a 3-sigma limit of Wr(2796)=0.01{\AA}. Combining known inclination and orientation angles of the star-forming disks, and resolved absorption profiles of the associated absorbers at rho < 35 kpc, we explore the parameter space for the opening angle theta_0 and the velocity field of large-scale galactic outflows as a function of z-height, v(z). We find that the absorption profiles of the MgII doublets and FeII series are compatible with the gas being either accelerated or decelerated, depending on theta_0, though accelerated outflows are valid only for a narrow range of theta_0. Under an acceleration scenario, we compare the derived $v(z)$ with predictions from Murray et al. (2011) and find that if the gas is being accelerateted by the radiation and ram pressure forces from super star clusters, then the efficiency of thermal energy input from a supernova explosion is epsilon <= 0.01.

A Spitzer IRAC Measure of the Zodiacal Light

astro-ph — Mon, 21 May 2012 00:41:11 +0000

The dominant non-instrumental background source for space-based infrared observatories is the zo- diacal light. We present Spitzer Infrared Array Camera (IRAC) measurements of the zodiacal light at 3.6, 4.5, 5.8, and 8.0 {\mu}m, taken as part of the instrument calibrations. We measure the changing surface brightness levels in approximately weekly IRAC observations near the north ecliptic pole (NEP) over the period of roughly 8.5 years. This long time baseline is crucial for measuring the annual sinusoidal variation in the signal levels due to the tilt of the dust disk with respect to the ecliptic, which is the true signal of the zodiacal light. This is compared to both Cosmic Background Explorer Diffuse Infrared Background Experiment (COBE DIRBE) data and a zodiacal light model based thereon. Our data show a few percent discrepancy from the Kelsall et al. (1998) model including a potential warping of the interplanetary dust disk and a previously detected overdensity in the dust cloud directly behind the Earth in its orbit. Accurate knowledge of the zodiacal light is important for both extragalactic and Galactic astronomy including measurements of the cosmic infrared background, absolute measures of extended sources, and comparison to extrasolar interplanetary dust models. IRAC data can be used to further inform and test future zodiacal light models.

An Interface for the Virtual Observatory of the University of Guanajuato

astro-ph — Mon, 21 May 2012 00:40:57 +0000

We present the first attempts to build a user-friendly interface for the Virtual Observatory of the University of Guanajuato. The data tables will be accessible to the public through PHP scripts and SQL database managers, such as MySQL and PostgreSQL, all administrated through phpMyAdmin and pgMyAdmin. Although it is not made public yet, this interface will be the basis upon which the final front end for our VO will be built. Furthermore, we present a preliminary version of a web front end to the publicly available stellar population synthesis code STARLIGHT (starlight.ufsc.br) which will be made available with our VO. This front end aims to provide an easy and flexible access to the code itself, letting users fit their own observed spectra with their preferred combination of physical and technical parameters, rather than making available only the results of fitting a specific sample of spectra with predefined parameters.

Cosmological solution of Machian gravity [Cross-Listing]

astro-ph — Mon, 21 May 2012 00:40:43 +0000

The standard model of cosmology predicts that more than 95% matter in the universe consists of dark components namely dark matter and dark energy. In spite of several attempts to measure these components, there is not a single direct observational evidence for these components till date. Hence, different alternate models of cosmology have been put forward by different authors. However, most of these models have their own problems. Therefore, in this paper, a new cosmological model has been proposed. This model is based on the Machian gravity model, which will be discussed in detail in a later paper. The model can provide an exactly similar cosmology as that of the standard cosmological model without demanding any ad-hoc dark matter or dark energy components. The paper shows that when the field equations from Machian gravity (a 5 dimensional model) are projected to the 4-dimensional space-time, some new mathematical terms arise in the equations that behave exactly like dark matter and dark energy. These mathematical terms come completely from the geometry of the universe and therefore these do not have any connection with the real matter. As the General theory of Relativity does not follow Mach’s principle, the FLRW model that is based on GR, cannot provide the correct solution to the cosmological model and demands extra forms of matter and energy to give any predictions consistent with the observations.

The sizes, masses and specific star-formation rates of massive galaxies at 1.3
astro-ph — Mon, 21 May 2012 00:40:32 +0000

We report the results of a comprehensive study of the relationship between galaxy size, stellar mass and specific star-formation rate (sSFR) at redshifts 1.3

Two distinct halo populations in the solar neighborhood. IV. Lithium abundances

astro-ph — Mon, 21 May 2012 00:38:22 +0000

We investigate if there is a difference in the lithium abundances of stars belonging to two halo populations of F and G main-sequence stars previously found to differ in [alpha/Fe] for the metallicity range -1.4 < [Fe/H] < -0.7. Li abundances are derived from the LiI 6707.8 A line measured in high-resolution spectra using MARCS model atmospheres. Furthermore, masses of the stars are determined from the logTeff – logg diagram by interpolating between Yonsei-Yale evolutionary tracks. There is no significant systematic difference in the lithium abundances of high- and low-alpha halo stars. For the large majority of stars with masses 0.7 < M/M_sun < 0.9 and heavy-element mass fractions 0.001 < Z < 0.006, the Li abundance is well fitted by a relation A(Li) = a0 + a1 M + a2 Z + a3 M Z, where a0, a1, a2, and a3 are constants. Extrapolating this relation to Z = 0 leads to a Li abundance close to the primordial value predicted from standard Big Bang nucleosynthesis calculations and the WMAP baryon density. The relation, however, does not apply to stars with [Fe/H] < -1.5. We suggest that metal-rich halo stars were formed with a Li abundance close to the primordial value, and that lithium in their atmospheres has been depleted in time with an approximately linear dependence on stellar mass and Z. The lack of a systematic difference in the Li abundances of high- and low-alpha stars indicates that an environmental effect is not important for the destruction of lithium.

130 GeV Gamma-Ray Line from Dark Matter Decay [Cross-Listing]

astro-ph — Mon, 21 May 2012 00:38:09 +0000

The 130 GeV gamma-ray line based on tentative analyses on the Fermi-LAT data is hard to be understood with dark matter annihilation in the conventional framework of the MSSM. We point out that it can be nicely explained with two body decay of a scalar dark matter ($\tilde{\phi}_{\rm DM}\rightarrow\gamma\gamma$) by the dimension 6 operator suppressed with the mass of the grand unification scale ($\sim 10^{16}$ GeV), ${\cal L}\supset|\tilde{\phi}_{\rm DM}|^2F_{\mu\nu}F^{\mu\nu}/M_{\rm GUT}^2$, in which the scalar dark matter $\tilde{\phi}_{\rm DM}$ develops a TeV scale vacuum expectation value. We propose a viable model, which can explain the 130 GeV gamma-ray line and also the abundance of $\tilde{\phi}_{\rm DM}$.

A divergence-cleaning scheme for cosmological SPMHD simulations

astro-ph — Mon, 21 May 2012 00:37:35 +0000

In magnetohydrodynamics (MHD), the magnetic field is evolved by the induction equation and coupled to the gas dynamics by the Lorentz force. We perform numerical smoothed particle magnetohydrodynamics (Spmhd) simulations and study the influence of a numerical magnetic divergence. For instabilities arising from divergence B related errors, we find the hyperbolic/parabolic cleaning scheme suggested by Dedner et al. 2002 to give good results and prevent numerical artifacts from growing. Additionally, we demonstrate that certain current Spmhd implementations of magnetic field regularizations give rise to unphysical instabilities in long-time simulations. We also find this effect when employing Euler potentials (divergenceless by definition), which are not able to follow the winding-up process of magnetic field lines properly. Furthermore, we present cosmological simulations of galaxy cluster formation at extremely high resolution including the evolution of magnetic fields. We show synthetic Faraday rotation maps and derive structure functions to compare them with observations. Comparing all the simulations with and without divergence cleaning, we are able to confirm the results of previous simulations performed with the standard implementation of MHD in Spmhd at normal resolution. However, at extremely high resolution, a cleaning scheme is needed to prevent the growth of numerical errors at small scales.

The bright-end of the luminosity function at z~9

astro-ph — Mon, 21 May 2012 00:37:24 +0000

We report new constraints on the galaxy luminosity function at z~9 based on observations carried out with ESO/VLT FORS2, HAWK-I and X-Shooter around the lensing cluster A2667, as part of our project aimed at selecting z~7-10 candidates accessible to spectroscopy. Only one J-dropout source was selected in this field fulfilling the color and magnitude criteria. This source was recently confirmed as a mid-z interloper based on X-Shooter spectroscopy. The depth and the area covered by our survey are well suited to set strong constraints on the bright-end of the galaxy luminosity function and hence on the star formation history at very high redshift. The non-detection of reliable J-dropout sources over the ~36arcmin2 field of view towards A2667 was used to carefully determine the lens-corrected effective volume and the corresponding upper-limit on the density of sources. The strongest limit is obtained for Phi(M_{1500}=-21.4+/-0.50)-19.7 with fixed alpha=-1.74 and Phi*=1.10×10^{-3}Mpc^{-3}. The corresponding star formation rate density should be rho_{SFR}<5.97×10^{-3}M_{solar}/yr/Mpc^{3} at z~9. These results are in good agreement with the most recent estimates already published in this range of redshift and for this luminosity domain. This new result confirms the decrease in the density of luminous galaxies at very high-redshift, hence providing strong constraints for the design of future surveys aiming to explore the very high-redshift Universe.

Measuring Space-Time Geometry over the Ages [Cross-Listing]

astro-ph — Mon, 21 May 2012 00:36:48 +0000

Theorists are often told to express things in the “observational plane”. One can do this for space-time geometry, considering “visual” observations of matter in our universe by a single observer over time, with no assumptions about isometries, initial conditions, nor any particular relation between matter and geometry, such as Einstein’s equations. Using observables as coordinates naturally leads to a parametrization of space-time geometry in terms of other observables, which in turn prescribes an observational program to measure the geometry. Under the assumption of vorticity-free matter flow we describe this observational program, which includes measurements of gravitational lensing, proper motion, and redshift drift. Only 15% of the curvature information can be extracted without long time baseline observations, and this increases to 35% with observations that will take decades. The rest would likely require centuries of observations. The formalism developed is exact, non-perturbative, and more general than the usual cosmological analysis.

Classification of the FRW universe with a cosmological constant and a perfect fluid of the equation of state $p = w\rho$ [Replacement]

astro-ph — Mon, 21 May 2012 00:36:01 +0000

We systematically study the evolution of the Friedmann-Robertson-Walker (FRW) universe coupled with a cosmological constant $\Lambda$ and a perfect fluid that has the equation of state $p=w\rho$, where $p$ and $\rho$ denote, respectively, the pressure and energy density of the fluid, and $w$ is an arbitrary real constant. Depending on the specific values of $w,\; \Lambda$, and the curvature $k$ of 3-dimensional space, we separate all of the solutions into various cases. In each case the main properties of the evolution are given in detail, including the periods of deceleration and/or acceleration, and the existence of big bang, big crunch, and big rip singularities. In some cases, errors in classification and interpretation appearing in standard textbooks have been corrected.

Parameterizing the flattening of galaxies rotation curves on expanding locally anisotropic backgrounds [Replacement]

astro-ph — Mon, 21 May 2012 00:35:36 +0000

In this work are discussed possible generalizations of the expanding locally anisotropic metric ansatz with respect to approximately Newtonian many body gravitational systems. This ansatz describes local point-like matter distributions on the expanding Universe also allowing for a covariant parameterization of gravitational interactions at intermediate length scales. As an example of applicability it is modelled a disk galaxy model matching the physical parameters of the galaxy UGC2885 and it is shown that, by fine-tuning the metric functional parameter, the flattening of the galaxy rotation curve is fully parameterized by this metric. It is further analysed the mass-energy density corrections due to the expanding anisotropic background being shown that although there are negative contributions within the galaxy plane the total mass-energy density is strictly positive. Outside the galaxy plane, by considering an anisotropic functional parameter, it is shown that the mass-energy density is also strictly positive.

Wheels of Fire IV. Star Formation and the Neutral Interstellar Medium in the Ring Galaxy AM0644-741 [Replacement]

astro-ph — Mon, 21 May 2012 00:35:04 +0000

We combine data from the ATNF and the SEST to investigate the neutral ISM in AM0644-741, a large and robustly star-forming ring galaxy. The galaxy’s ISM is concentrated in the 42-kpc diameter starburst ring, but appears dominated by atomic gas, with a global molecular fraction (f_mol) of only 7.9%. Apart from the starburst peak, the gas ring is stable against the growth of gravitational instabilities (Q_gas=2-7). Including stars lowers Q overall, but not enough to make Q100 Myr confinement time in the starburst ring, which enhances the destructive effects of embedded massive stars and supernovae. As a result, the ring’s molecular ISM becomes dominated by small clouds where star formation is most intense, causing H2 to be underestimated by 12CO line fluxes: in effect X(CO) >> X(Gal) despite the ring’s solar metallicity. The observed large HI component is primarily a low density photodissociation product, i.e., a tracer rather than a precursor of massive star formation. Such an “over-cooked” ISM may be a general characteristic of evolved starburst ring galaxies.

FRW Cosmology in Ghost Free Massive Gravity [Replacement]

astro-ph — Mon, 21 May 2012 00:34:30 +0000

We study FRW homogeneous cosmological solutions in the recently found ghost free massive gravity. In previous works it was shown that when the additional extra metric, needed to generate the mass term, is taken as non-dynamical and flat, no homogeneous FRW cosmology exists. We show that, when the additional metric is a dynamical field, a perfectly safe FRW universe exists. FRW solutions fall in two branches. In the first branch the massive deformation is equivalent to an effectively generated cosmological constant whose scale is determined by the graviton mass. The second branch is quite rich: we have FRW cosmology in the presence of a “gravitational” fluid. The control parameter xi is the ratio of the two conformal factors. When xi is large, generically the cosmological evolution greatly differs from GR at the early time. In the small xi region, the evolution is similar to GR and the universe flows at late time toward an attractor represented by a dS phase.

The density profiles of Dark Matter halos in Spiral Galaxies [Replacement]

astro-ph — Mon, 21 May 2012 00:34:04 +0000

In spiral galaxies, we explain their non-Keplerian rotation curves (RCs) by means of a non-luminous component embedding their stellar-gaseous disks. Understanding the detailed properties of this component (labelled Dark Matter, DM) is one of the most pressing issues of Cosmology. We investigate the recent relationship (claimed by Walker et al. 2010, hereafter W+10) between $r$, the galaxy radial coordinate, and $V_h(r)$, the dark halo contribution to the circular velocity at $r$, {\it a}) in the framework of the Universal Rotation Curve (URC) paradigm and directly {\it b}) by means of the kinematics of a large sample of DM dominated spirals. We find a general agreement between the W+10 claim, the distribution of DM emerging from the URC and that inferred in the (low luminosity) objects of our sample. We show that such a phenomenology, linking the spiral’s luminosity, radii and circular velocities, implies an evident inconsistency with (naive) predictions in the $\Lambda$ Cold Dark Matter ($\Lambda$CDM) scenario.

The Strong Multifield Slowroll Condition and Spiral Inflation [Replacement]

astro-ph — Mon, 21 May 2012 00:33:39 +0000

We point out the existing confusions about the slowroll parameters and conditions for multifield inflation. If one requires the fields to roll down the gradient flow, we find that only articles adopting the Hubble slowroll expansion are on the right track, and a correct condition can be found in a recent book by Liddle and Lyth. We further analyze this condition and show that the gradient flow requirement is stronger than just asking for a slowly changing, quasi-de Sitter solution. Therefore it is possible to have a multifield slowroll model that does not follow the gradient flow. Consequently, it no longer requires the gradient to be small. It even bypasses the first slowroll condition and some related no-go theorems from string theory. We provide the “spiral inflation” as a generic blueprint of such inflation model and show that it relies on a monodromy locus—a common structure in string theory effective potentials.

Highly Ionized Collimated Outflow from HE 0238 – 1904 [Replacement]

astro-ph — Mon, 21 May 2012 00:33:14 +0000

We present a detailed analysis of a highly ionized, multiphased and collimated outflowing gas detected through O V, O VI, Ne VIII and Mg X absorption associated with the QSO HE 0238 – 1904 (z_em ~ 0.629). Based on the similarities in the absorption line profiles and estimated covering fractions, we find that the O VI and Ne VIII absorption trace the same phase of the absorbing gas. Simple photoionization models can reproduce the observed N(Ne VIII), N(O VI) and N(Mg X) from a single phase whereas the low ionization species (e.g. N III, N IV, O IV) originate from a different phase. The measured N(Ne VIII)/N(O VI) ratio is found to be remarkably similar (within a factor of ~ 2) in several individual absorption components kinematically spread over ~ 1800 km/s. Under photoionization this requires a fine tuning between hydrogen density (nH) and the distance of the absorbing gas from the QSO. Alternatively this can also be explained by collisional ionization in hot gas with T > 10^{5.7} K. Long-term stability favors the absorbing gas being located outside the broad line region (BLR). We speculate that the collimated flow of such a hot gas could possibly be triggered by the radio jet interaction.

The VMC Survey. V. First results for Classical Cepheids [Replacement]

astro-ph — Mon, 21 May 2012 00:32:45 +0000

The VISTA Magellanic Cloud (VMC, PI M.R. Cioni) survey is collecting deep Ks-band time-series photometry of the pulsating variable stars hosted by the system formed by the two Magellanic Clouds (MCs) and the “bridge” connecting them. In this paper we present the first results for Classical Cepheids, from the VMC observations of two fields in the Large Magellanic Cloud (LMC). The VMC Ks-band light curves of the Cepheids are well sampled (12-epochs) and of excellent precision. We were able to measure for the first time the Ks magnitude of the faintest Classical Cepheids in the LMC (Ks\sim17.5 mag), which are mostly pulsating in the First Overtone (FO) mode, and to obtain FO Period-Luminosity (PL), Period-Wesenheit (PW), and Period-Luminosity-Color (PLC) relations, spanning the full period range from 0.25 to 6 day. Since the longest period Cepheid in our dataset has a variability period of 23 day, we have complemented our sample with literature data for brighter F Cepheids. On this basis we have built a PL relation in the Ks band that, for the first time, includes short period pulsators, and spans the whole range from 1.6 to 100 days in period. We also provide the first ever empirical PW and PLC relations using the (V-Ks) color and time-series Ks photometry. The very small dispersion (\sim0.07 mag) of these relations makes them very well suited to study the three-dimensional (3D) geometry of the Magellanic system. The use of “direct” (parallax- and Baade-Wesselink- based) distance measurements to both Galactic and LMC Cepheids, allowed us to calibrate the zero points of the PL, PW, and PLC relations obtained in this paper, and in turn to estimate an absolute distance modulus of (m-M)0=18.46\pm0.03 for the LMC. This result is in agreement with most of the latest literature determinations based on Classical Cepheids.

The parsec-scale jet of PKS 1749+096 [Replacement]

astro-ph — Mon, 21 May 2012 00:32:22 +0000

PKS 1749+096 is a BL Lac object showing weak extended jet emission to the northeast of the compact VLBI core on parsec scales. We aim at better understanding the jet kinematics and variability of this source and finding clues that may applicable to other BL Lac objects. The jet was studied with multi-epoch multi-frequency high-resolution VLBI observations. The jet is characterized by a one-sided curved morphology at all epochs and all frequencies. The VLBI core, located at the southern end of the jet, was identified based on its spectral properties. The equipartition magnetic field of the core was investigated, through which we derived a Doppler factor of 5, largely consistent with that derived from kinematics (component C5). The study of the detailed jet kinematics at 22 and 15 GHz, spanning a period of more than 10 years, indicates the possible existence of a bimodal distribution of the jet apparent speed. Ballistic and non-ballistic components are found to coexist in the jet. Superluminal motions in the range of 5-21 c were measured in 11 distinct components. We estimated the physical jet parameters with the minimum Lorentz factor of 10.2 and Doppler factors in the range of 10.2-20.4 (component C5). The coincidence in time of the component’s ejection and flares supports the idea that, at least in PKS 1749+096, ejection of new jet components is connected with major outbursts in flux density. For the best-traced component (C5) we found that the flux density decays rapidly as it travels downstream the jet, accompanied by a steepening of its spectra, which argues in favor of a contribution of inverse Compton cooling. These properties make PKS 1749+096 a suitable target for an intensive monitoring to decipher the variability phenomenon of BL Lac objects.

Warm Dark Matter in Low Scale Left-Right Theory [Replacement]

astro-ph — Mon, 21 May 2012 00:31:52 +0000

We investigate the viability of having dark matter in the minimal left-right symmetric theory. We find the lightest right-handed neutrino with a mass around keV as the only viable candidate consistent with a TeV scale of left-right symmetry. In order to account for the correct relic density with such low scales, the thermal overproduction of the dark matter in the early universe is compensated by a sufficient late entropy production due to late decay of heavier right-handed neutrinos. We point out that the presence of the right-handed charge-current interactions, operative around the QCD phase transition, has a crucial impact on the amount of dilution, as does the nature of the phase transition itself. A careful numerical study, employing the Boltzmann equations, reveals the existence of a narrow window for the right-handed gauge boson mass, possibly within the reach of LHC (in disagreement with a previous study). We also elaborate on a variety of astrophysical, cosmological and low energy constraints on this scenario.

[CII] line emission in massive star-forming galaxies at z=4.7 [Replacement]

astro-ph — Mon, 21 May 2012 00:31:32 +0000

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the [CII] 157.7micron fine structure line and thermal dust continuum emission from a pair of gas-rich galaxies at z=4.7, BR1202-0725. This system consists of a luminous quasar host galaxy and a bright submm galaxy (SMG), while a fainter star-forming galaxy is also spatially coincident within a 4″ (25 kpc) region. All three galaxies are detected in the submm continuum, indicating FIR luminosities in excess of 10^13 Lsun for the two most luminous objects. The SMG and the quasar host galaxy are both detected in [CII] line emission with luminosities, L([CII]) = (10.0 +/- 1.5)x10^9 Lsun and L([CII]) = (6.5+/-1.0)x10^9 Lsun, respectively. We estimate a luminosity ratio, L([CII])/L(FIR) = (8.3+/-1.2)x10^-4 for the starburst SMG to the North, and L([CII])/L(FIR) = (2.5+/-0.4)x10^-4 for the quasar host galaxy, in agreement with previous high-redshift studies that suggest lower [CII]-to-FIR luminosity ratios in quasars than in starburst galaxies. The third fainter object with a flux density, S(340GHz) = 1.9+/-0.3 mJy, is coincident with a Ly-Alpha emitter and is detected in HST ACS F775W and F814W images but has no clear counterpart in the H-band. Even if this third companion does not lie at a similar redshift to BR1202-0725, the quasar and the SMG represent an overdensity of massive, infrared luminous star-forming galaxies within 1.3 Gyr of the Big Bang.

Deuterium at high-redshift: Primordial abundance in the zabs = 2.621 damped Ly-alpha system towards CTQ247

astro-ph — Fri, 18 May 2012 00:58:01 +0000

The detection of neutral deuterium in the low-metallicity damped Lyman-{\alpha} system at zabs = 2.621 towards the quasar CTQ247 is reported. Using a high signal-to-noise and high spectral resolution (R = 60000) spectrum from the Very Large Telescope Ultraviolet and Visual Echelle Spectrograph, we precisely measure the deuterium-to-oxygen ratio log N(DI)/N(OI) = 0.74+/-0.04, as well as the overall oxygen abundance, log N(OI)/N(HI)=-5.29+/-0.10 (or equivalently [O/H]=-1.99+/-0.10 with respect to the solar value). Assuming uniform metallicity throughout the system, our measurement translates to (D/H) = (2.8+0.8 -0.6)x10^-5. This ratio is consistent within errors (<0.4sigma) with the primordial ratio, (D/H)p = (2.59+/-0.15)x10^-5, predicted by standard Big-Bang Nucleosynthesis using the WMAP7 value of the cosmological density of baryons (100 Omega_b h^2 = 2.249+/-0.056). The DI absorption lines are observed to be broader than the OI absorption lines. From a consistent fit of the profiles we derive the turbulent broadening to be 5.2 km/s and the temperature of the gas to be T = 8800+/-1500 K, corresponding to a warm neutral medium.

HerMES: Candidate Gravitationally Lensed Galaxies and Lensing Statistics at Submillimeter Wavelengths

astro-ph — Fri, 18 May 2012 00:57:19 +0000

We present a list of 13 candidate gravitationally lensed submillimeter galaxies (SMGs) from 95 square degrees of the Herschel Multi-tiered Extragalactic Survey, a surface density of 0.14\pm0.04deg^{-2}. These sources have 500um flux densities (S_500) greater than 100mJy. Follow-up observations confirm gravitational lensing in 9 of the 13 systems (70%); the lensing status of the four remaining sources is undetermined. We also present a supplementary sample of 29 (0.31\pm0.06deg^{-2}) gravitationally lensed SMG candidates with S_500=80–100mJy, which are expected to contain a higher fraction of interlopers than the primary candidates. The number counts of the candidate lensed galaxies are consistent with a simple statistical model of the lensing rate, which uses a foreground matter distribution, the intrinsic SMG number counts, and an assumed SMG redshift distribution. The model predicts that 43–83% of our S_500>100mJy candidates are strongly gravitationally lensed, with the brightest sources being the most robust; this is consistent with the observational data. Our statistical model also predicts that, on average, lensed galaxies with S_500=100mJy are magnified by factors of ~6, with brighter galaxies having progressively higher average magnification. 50% of the sources are expected to have intrinsic 500um flux densities less than 30mJy. Thus, samples of strongly gravitationally lensed SMGs, such as those presented here, probe below the nominal Herschel detection limit at 500um. They are ideal targets for the detailed study of the physical conditions in distant dusty, star-forming galaxies, with unprecedented spatial resolution achieved due to the lensing magnification.

The Optically Unbiased GRB Host (TOUGH) survey. IV. Lyman-alpha emitters

astro-ph — Fri, 18 May 2012 00:56:59 +0000

We report the results of a spectroscopic search for Lyman-alpha emission from gamma-ray burst host galaxies. Based on the well-defined TOUGH sample of 69 X-ray selected Swift GRBs, we have targeted the hosts of a subsample of 20 GRBs known from afterglow spectroscopy to be in the redshift range 1.8-4.5. We detect Lya emission from 7 out of the 20 hosts, with the typical limiting 3sigma line flux being 8E-18 erg/cm2/s, corresponding to a Lya luminosity of 6E41 erg/s at z=3. The Lya luminosities for the 7 hosts in which we detect Lya emission are in the range (0.6-2.3)E42 erg/s corresponding to star-formation rates of 0.6-2.1 Msun/yr (not corrected for extinction). The rest-frame Lya equivalent widths (EWs) for the 7 hosts are in the range 9-40A. For 6 of the 13 hosts for which Lya is not detected we place fairly strong 3sigma upper limits on the EW (<20A), while for others the EW is either unconstrained or has a less constraining upper limit. We find that the distribution of Lya EWs is inconsistent with being drawn from the Lya EW distribution of bright Lyman break galaxies at the 98.3% level, in the sense that the TOUGH hosts on average have larger EWs than bright LBGs. We can exclude an early indication, based on a smaller, heterogeneous sample of pre-Swift GRB hosts, that all GRB hosts are Lya emitters. We find that the TOUGH hosts on average have lower EWs than the pre-Swift GRB hosts, but the two samples are only inconsistent at the 92% level. The velocity centroid of the Lya line is redshifted by 200-700 km/s with respect to the systemic velocity, similar to what is seen for LBGs, possibly indicating star-formation driven outflows from the host galaxies. There seems to be a trend between the Lya EW and the optical to X-ray spectral index of the afterglow (beta_OX), hinting that dust plays a role in the observed strength and even presence of Lya emission. [ABRIDGED]

A new, precise measurement of the primordial abundance of Deuterium

astro-ph — Fri, 18 May 2012 00:55:39 +0000

The metal-poor damped Lyman alpha (DLA) system at z = 3.04984 in the QSO SDSSJ1419+0829 has near-ideal properties for an accurate determination of the primordial abundance of deuterium, (D/H)_p. We have analysed a high-quality spectrum of this object with software specifically designed to deduce the best fitting value of D/H and to assess comprehensively the random and systematic errors affecting this determination. We find (D/H)_DLA = (2.535 +/-0.05) x 10^(-5), which in turn implies Omega_b h^2 = 0.0223 +/- 0.0009, in very good agreement with Omega_b h^2 (CMB) = 0.0222 +/- 0.0004 deduced from the angular power spectrum of the cosmic microwave background. If the value in this DLA is indeed the true (D/H)_p produced by Big-Bang nucleosynthesis (BBN), there may be no need to invoke non-standard physics nor early astration of D to bring together Omega_b h^2 (BBN) and Omega_b h^2 (CMB). The scatter between most of the reported values of (D/H)_p in the literature may be due largely to unaccounted systematic errors and biases. Further progress in this area will require a homogeneous set of data comparable to those reported here and analysed in a self-consistent manner. Such an endeavour, while observationally demanding, has the potential of improving our understanding of BBN physics, including the relevant nuclear reactions, and the subsequent processing of 4He and 7Li through stars.

IDCS J1426+3508: Discovery of a Massive, IR-Selected Galaxy Cluster at z = 1.75

astro-ph — Fri, 18 May 2012 00:55:25 +0000

We report the discovery of an IR-selected massive galaxy cluster in the IRAC Distant Cluster Survey (IDCS). We present new data from the Hubble Space Telescope and the W. M. Keck Observatory that spectroscopically confirm IDCS J1426+3508 at z=1.75. Moreover, the cluster is detected in archival Chandra data as an extended X-ray source, comprising 54 counts after the removal of point sources. We calculate an X-ray luminosity of L{0.5-2 keV} = (5.5 +/- 1.2) X 1e44 ergs/s within r = 60 arcsec (~1 Mpc diameter), which implies M_{200,L_x} = (5.6 +/- 1.6) X 1e14 Msun. IDCS J1426+3508 appears to be an exceptionally massive cluster for its redshift.

IDCS J1426.5+3508: Sunyaev-Zel’dovich Measurement of a Massive IR-selected Cluster at z=1.75

astro-ph — Fri, 18 May 2012 00:55:07 +0000

We report 31 GHz CARMA observations of IDCS J1426.5+3508, an infrared-selected galaxy cluster at z = 1.75. A Sunyaev-Zel’dovich decrement is detected towards this cluster, indicating a total mass of M200 = (4.3 +/- 1.1) x 10^{14} Msun in agreement with the approximate X-ray mass of ~5 x 10^{14} Msun. IDCS J1426.5+3508 is by far the most distant cluster yet detected via the Sunyaev-Zel’dovich effect, and the most massive z >= 1.4 galaxy cluster found to date. Despite the mere ~1% probability of finding it in the 8.82 deg^2 IRAC Distant Cluster Survey, IDCS J1426.5+3508 is not completely unexpected in LCDM once the area of large, existing surveys is considered. IDCS J1426.5+3508 is, however, among the rarest, most extreme clusters ever discovered, and indeed is an evolutionary precursor to the most massive known clusters at all redshifts. We discuss how imminent, highly sensitive Sunyaev-Zel’dovich experiments will complement infrared techniques for statistical studies of the formation of the most massive galaxy clusters in the z > 1.5 Universe, including potential precursors to IDCS J1426.5+3508.

IDCS J1426.5+3508: Cosmological implications of a massive, strong lensing cluster at Z = 1.75

astro-ph — Fri, 18 May 2012 00:54:51 +0000

The galaxy cluster IDCS J1426.5+3508 at z = 1.75 is the most massive galaxy cluster yet discovered at z > 1.4 and the first cluster at this epoch for which the Sunyaev-Zel’Dovich effect has been observed. In this paper we report on the discovery with HST imaging of a giant arc associated with this cluster. The curvature of the arc suggests that the lensing mass is nearly coincident with the brightest cluster galaxy, and the color is consistent with the arc being a star-forming galaxy. We compare the constraint on M200 based upon strong lensing with Sunyaev-Zel’Dovich results, finding that the two are consistent if the redshift of the arc is z > 3. Finally, we explore the cosmological implications of this system, considering the likelihood of the existence of a strongly lensing galaxy cluster at this epoch in an LCDM universe. While the existence of the cluster itself can potentially be accomodated if one considers the entire volume covered at this redshift by all current high-redshift cluster surveys, the existence of this strongly lensed galaxy greatly exacerbates the long-standing giant arc problem. For standard LCDM structure formation and observed background field galaxy counts this lens system should not exist. Specifically, there should be no giant arcs in the entire sky as bright in F814W as the observed arc for clusters at z \geq 1.75, and only \sim 0.3 as bright in F160W as the observed arc. If we relax the redshift constraint to consider all clusters at z \geq 1.5, the expected number of giant arcs rises to \sim15 in F160W, but the number of giant arcs of this brightness in F814W remains zero. These arc statistic results are independent of the mass of IDCS J1426.5+3508. We consider possible explanations for this discrepancy.

The Lick AGN Monitoring Project 2011: Dynamical Modeling of the Broad Line Region in Mrk 50

astro-ph — Fri, 18 May 2012 00:54:32 +0000

We present dynamical modeling of the broad line region (BLR) in the Seyfert 1 galaxy Mrk 50 using reverberation mapping data taken as part of the Lick AGN Monitoring Project (LAMP) 2011. We model the reverberation mapping data directly, constraining the geometry and kinematics of the BLR, as well as deriving a black hole mass estimate that does not depend on a normalizing factor or virial coefficient. We find that the geometry of the BLR in Mrk 50 is a nearly face-on thick disk, with a mean radius of 9.6(+1.2,-0.9) light days, a width of the BLR of 6.9(+1.2,-1.1) light days, and a disk opening angle of 25\pm10 degrees above the plane. We also constrain the inclination angle to be 9(+7,-5) degrees, close to face-on. Finally, the black hole mass of Mrk 50 is inferred to be log10(M(BH)/Msun) = 7.57(+0.44,-0.27). By comparison to the virial black hole mass estimate from traditional reverberation mapping analysis, we find the normalizing constant (virial coefficient) to be log10(f) = 0.78(+0.44,-0.27), consistent with the commonly adopted mean value of 0.74 based on aligning the M(BH)-{\sigma}* relation for AGN and quiescent galaxies. While our dynamical model includes the possibility of a net inflow or outflow in the BLR, we cannot distinguish between these two scenarios.

Spherically Symmetric Inflation [Cross-Listing]

astro-ph — Fri, 18 May 2012 00:54:15 +0000

It is shown in this letter that in the framework of an inhomogeneous geometry and a massive non self-interacting scalar field with spherical symmetry, one needs a homogeneous patch bigger than a dizaine of horizons in order to start inflation. The results are completly independent of initial conditions on the spatial distribution of the scalar field. The initial condition on the metric parameters are also justified. This is a generalization of the results obtained in Ref.[1], showing that their conclusions are rather robust.

HI Power Spectra and the Turbulent ISM of Dwarf Irregular Galaxies

astro-ph — Fri, 18 May 2012 00:53:31 +0000

HI spatial power spectra (PS) were determined for a sample of 24 nearby dwarf irregular galaxies selected from the LITTLE THINGS (Local Irregulars That Trace Luminosity Extremes – The HI Nearby Galaxy Survey) sample. The two-dimensional (2D) power spectral indices asymptotically become a constant for each galaxy when a significant part of the line profile is integrated. For narrow channel maps, the PS become shallower as the channel width decreases, and this shallowing trend continues to our single channel maps. This implies that even the highest velocity resolution of 1.8 km/s is not smaller than the thermal dispersion of the coolest, widespread HI component. The one-dimensional PS of azimuthal profiles at different radii suggest that the shallower PS for narrower channel width is mainly contributed by the inner disks, which indicates that the inner disks have proportionally more cooler HI than the outer disks. Galaxies with lower luminosity (M_B > -14.5 mag) and star formation rate (SFR, log(SFR (M\odot/yr)) < -2.1) tend to have steeper PS, which implies that the HI line-of-sight depths can be comparable with the radial length scales in low mass galaxies. A lack of a correlation between the inertial-range spectral indices and SFR surface density implies that either non-stellar power sources are playing a fundamental role in driving the interstellar medium (ISM) turbulent structure, or the nonlinear development of turbulent structures has little to do with the driving sources.

Constraining stellar assembly and AGN feedback at the peak epoch of star formation

astro-ph — Fri, 18 May 2012 00:51:50 +0000

We study stellar assembly and feedback from active galactic nuclei (AGN) around the epoch of peak star formation (1

Progenitor mass constraints for core-collapse supernovae from correlations with host galaxy star formation

astro-ph — Fri, 18 May 2012 00:51:34 +0000

Using H-alpha emission as a tracer of on-going (<16 Myr old) and near-UV emission as a tracer of recent (16-100 Myr old) star formation (SF), we present constraints on core-collapse (CC) supernova (SN) progenitors through their association with SF regions. We present statistics of a large sample of SNe; 163.5 type II (58 IIP, 13 IIL, 13.5 IIb, 19 IIn and 12 'impostors') and 96.5 type Ib/c (39.5 Ib and 52 Ic). Using pixel statistics our main findings and conclusions are: 1) An increasing progenitor mass sequence is observed, implied from an increasing association of SNe to host galaxy H-alpha emission. This commences with the type Ia (SNIa) showing the weakest association, followed by the SNII, then the SNIb, with the SNIc showing the strongest correlation to SF regions. Thus our progenitor mass sequence runs Ia-II-Ib-Ic. 2) Overall SNIbc are found to occur nearer to bright HII regions than SNII. This implies that the former have shorter stellar lifetimes thus arising from more massive progenitor stars. 3) While SNIIP do not closely follow the on-going SF, they accurately trace the recent formation. This implies that their progenitors arise from stars at the low end of the CC SN mass sequence, consistent with direct detections of progenitors in pre-explosion imaging. 4) Similarly SNIIn trace recent but not the on-going SF. This implies that, contrary to the general consensus, the majority of these SNe do not arise from the most massive stars. Results and constraints are also presented for the less numerous SNIIL, IIb, and 'impostors'. Finally we present analysis of possible biases in the data, the results of which argue strongly against any selection effects that could explain the relative excess of SNIbc within bright HII regions. Thus intrinsic progenitor differences in the sense of the mass sequence we propose remain the most plausible explanation of our findings.

Gas Accretion is Dominated by Warm Ionized Gas in Milky Way-Mass Galaxies at z ~ 0

astro-ph — Fri, 18 May 2012 00:50:40 +0000

We perform high-resolution hydrodynamic simulations of a Milky Way-mass galaxy in a fully cosmological setting using the adaptive mesh refinement code, Enzo, and study the kinematics of gas in the simulated galactic halo. We find that the gas inflow occurs mostly along filamentary structures in the halo. The warm-hot (10^5 K < T 10^6 K) ionized gases are found to dominate the overall mass accretion in the system (with dM/dt = 3-5 M_solar/yr) over a large range of distances, extending from the virial radius to the vicinity of the disk. Most of the inflowing gas (by mass) does not cool, and the small fraction that manages to cool does so primarily close to the galaxy (R <~ 20 kpc), perhaps comprising the neutral gas that may be detectable as, e.g., high-velocity clouds. The neutral clouds are embedded within larger, accreting filamentary flows, and represent only a small fraction of the total mass inflow rate. The inflowing gas has relatively low metallicity (Z/Z_solar < 0.2). The outer layers of the filamentary inflows are heated due to compression as they approach the disk. In addition to the inflow, we find high-velocity, metal-enriched outflows of hot gas driven by supernova feedback. Our results are consistent with observations of halo gas at low z.

The Infrared Light Curve of SN 2011fe in M101 and the Distance to M101

astro-ph — Fri, 18 May 2012 00:50:15 +0000

We present near infra-red light curves of supernova (SN) 2011fe in M101, including 34 epochs in H band starting fourteen days before maximum brightness in the B-band. The light curve data were obtained with the WIYN High-Resolution Infrared Camera (WHIRC). When the data are calibrated using templates of other Type Ia SNe, we derive an apparent H-band magnitude at the epoch of B-band maximum of 10.85 \pm 0.04. This implies a distance modulus for M101 that ranges from 28.86 to 29.17 mag, depending on which absolute calibration for Type Ia SNe is used.

Star Formation in the First Galaxies I: Collapse Delayed by Lyman-Werner Radiation

astro-ph — Fri, 18 May 2012 00:48:49 +0000

We investigate the process of metal-free star formation in the first galaxies with a high-resolution cosmological simulation. We consider the cosmologically motivated scenario in which a strong molecule-destroying Lyman-Werner (LW) background inhibits effective cooling in low-mass haloes, delaying star formation until the collapse or more massive haloes. Only when molecular hydrogen (H2) can self-shield from LW radiation, which requires a halo capable of cooling by atomic line emission, will star formation be possible. To follow the formation of multiple gravitationally bound objects, at high gas densities we introduce sink particles which accrete gas directly from the computational grid. We find that in a 1 Mpc^3 (comoving) box, runaway collapse first occurs in a 3×10^7 M_sun dark matter halo at z~12 assuming a background intensity of J21=100. Due to a runaway increase in the H2 abundance and cooling rate, a self-shielding, supersonically turbulent core develops abruptly with ~10^4 M_sun in cold gas available for star formation. We analyze the formation of this self-shielding core, the character of turbulence, and the prospects for star formation. Due to a lack of fragmentation on scales we resolve, we argue that LW-delayed metal-free star formation in atomic cooling haloes is very similar to star formation in primordial minihaloes, although in making this conclusion we ignore internal stellar feedback. Finally, we briefly discuss the detectability of metal-free stellar clusters with the James Webb Space Telescope.

A Brightest Cluster Galaxy with an Extremely Large Flat Core

astro-ph — Fri, 18 May 2012 00:48:33 +0000

Hubble Space Telescope images of the galaxy cluster Abell 2261, obtained as part of the Cluster Lensing And Supernova survey with Hubble, show that the brightest galaxy in the cluster, A2261-BCG, has the largest core yet detected in any galaxy. The cusp radius of A2261-BCG is 3.2 kpc, twice as big as the next largest core known, and ~3x bigger than those typically seen in the most luminous BCGs. The morphology of the core in A2261-BCG is also unusual, having a flat or even slightly-depressed interior surface brightness profile, rather than the typical shallow cusp. This implies that the galaxy has a core with constant or even centrally decreasing stellar density. Interpretation of the core as an end product of the “scouring” action of a binary supermassive black hole implies a total black hole mass ~1E+10 M_sun from the extrapolation of most relationships between core structure and black hole mass. The core falls 1-sigma above the cusp-radius versus galaxy luminosity relation. Its large size in real terms, and the extremely large black hole mass required to generate it, raise the possibility that the core has been enlarged by additional processes, such as the ejection of the black holes that originally generated the core. The flat central stellar density profile is consistent with this hypothesis. The core is also displaced by 0.7 kpc from the center of the surrounding envelope, consistent with a local dynamical perturbation of the core.

Spectroscopy of extended Ly\alpha\ envelopes around z=4.5 quasars

astro-ph — Fri, 18 May 2012 00:46:26 +0000

What are the frequency, shape, kinematics, and luminosity of Ly\alpha\ envelopes surrounding radio-quiet quasars at high redshift, and is the luminosity of these envelopes related to that of the quasar or not? As a first step towards answering these questions, we have searched for Ly\alpha\ envelopes around six radio-quiet quasars at z~4.5, using deep spectra taken with the FORS2 spectrograph attached to the UT1 of the Very Large Telescope (VLT). Using the multi-slit mode allows us to observe several point spread function stars simultaneously with the quasar, and to remove the point-like emission from the quasar, unveiling the faint underlying Ly\alpha\ envelope with unprecedented depth. An envelope is detected around four of the six quasars, which suggests that these envelopes are very frequent. Their diameter varies in the range 26

Oxygen and nitrogen abundances of HII regions in six spiral galaxies

astro-ph — Fri, 18 May 2012 00:45:43 +0000

Spectroscopic observations of 63 HII regions in six spiral galaxies (NGC 628, NGC 783, NGC 2336, NGC 6217, NGC 7331, and NGC 7678) were carried out with the 6-meter telescope (BTA) of Russian Special Astrophysical Observatory with the Spectral Camera attached to the focal reducer SCORPIO in the multislit mode with a dispersion of 2.1A/pixel and a spectral resolution of 10A. These observations were used to estimate the oxygen and nitrogen abundances and the electron temperatures in HII regions through the recent variant of the strong line method (NS calibration). The parameters of the radial distribution (the extrapolated central intercept value and the gradient) of the oxygen and nitrogen abundances in the disks of spiral galaxies NGC 628, NGC 783, NGC 2336, NGC 7331, and NGC 7678 have been determined. The abundances in the NGC 783, NGC 2336, NGC 6217, and NGC 7678 are measured for the first time. Galaxies from our sample follow well the general trend in the luminosity – central metallicity diagram for spiral and irregular galaxies.

Relativistic jet models for two low-luminosity radio galaxies: evidence for backflow?

astro-ph — Fri, 18 May 2012 00:45:29 +0000

We show that asymmetries in total intensity and linear polarization between the radio jets and counter-jets in two lobed Fanaroff-Riley Class I (FR I) radio galaxies, B2 0206+35 (UGC 1651) and B2 0755+37 (NGC 2484), can be accounted for if these jets are intrinsically symmetrical, with decelerating relativistic outflows surrounded by mildly relativistic backflows. Our interpretation is motivated by sensitive, well-resolved Very Large Array imaging which shows that both jets in both sources have a two-component structure transverse to their axes. Close to the jet axis, a centrally-darkened counter-jet lies opposite a centrally-brightened jet, but both are surrounded by broader collimated emission that is brighter on the counter-jet side. We have adapted our previous models of FR I jets as relativistic outflows to include an added component of symmetric backflow. We find that the observed radio emission, after subtracting contributions from the extended lobes, is well described by models in which decelerating outflows with parameters similar to those derived for jets in plumed FR I sources are surrounded by backflows containing predominantly toroidal magnetic fields. These return to within a few kpc of the galaxies with velocities of roughly 0.25c and radiate with a synchrotron spectral index close to 0.55. We discuss whether such backflow is to be expected in lobed FR I sources and suggest ways in which our hypothesis can be tested by further observations.

The analysis of the hydrogen broad Balmer line ratios: possible implications to the physical properties of the BLR of AGN

astro-ph — Fri, 18 May 2012 00:44:54 +0000

We analyze the ratios of the broad hydrogen Balmer emission lines (from H\alpha to H\epsilon) in the context of estimating the physical conditions in the broad line region (BLR) of active galactic nuclei (AGN). The Balmer emission lines are obtained in three ways: i) using photoionization models obtained by a spectral synthesis code CLOUDY; ii) calculated using the recombination theory for hydrogenic ions; iii) measured from the sample of observed spectra taken from the Sloan Digital Sky Survey database. We investigate the Balmer line ratios in the frame of the so called Boltzmann-plot (BP), analyzing physical conditions of the emitting plasma for which we could use the BP method. The BP considers the ratio of Balmer lines normalized to the atomic data of the corresponding line transition, and is in that way different from the Balmer decrement. We found that for a certain range of thermodynamic parameters, there are objects that follow the BP. These AGN may have a BLR consisting of mostly high density plasma.

On the Validity of Cosmological Fisher Matrix Forecasts

astro-ph — Fri, 18 May 2012 00:42:26 +0000

We present a comparison of Fisher matrix forecasts for cosmological probes with Monte Carlo Markov Chain (MCMC) posterior likelihood estimation methods. We analyse the performance of future Dark Energy Task Force (DETF) stage-III and stage-IV dark-energy surveys using supernovae, baryon acoustic oscillations and weak lensing as probes. We concentrate in particular on the dark-energy equation of state parameters $w_0$ and $w_a$. For forecasts with fixed $w_a=0$, there is no qualitative discrepancy between the Fisher matrix approximation and the full likelihood via MCMC exploration, although there are significant quantitative differences; when marginalising over $w_a$ however, we find considerable disagreement between the two methods, since for geometrical probes the Fisher matrix can not reproduce the highly non-elliptical shape of the likelihood function. More quantitatively, the Fisher method overestimates the DETF figure of merit (FoM) for purely geometrical probes by a factor of up to seven. Even in the cases including additional information from structure formation, such as weak lensing, where the likelihood is fairly elliptical, the posterior probability contours from the Fisher matrix estimation are too small: the resulting FoM is biased low by a factor of two. We then explore non-linear transformations resulting in physically-motivated parameters and investigate whether these parameterisations exhibit a Gaussian behaviour. We conclude that, especially for the purely geometrical probes, but also for tests of structure formation, the Fisher matrix is not the appropriate tool to produce reliable forecasts.

Big Bang nucleosynthesis with a non-Maxwellian distribution [Cross-Listing]

astro-ph — Fri, 18 May 2012 00:40:52 +0000

The abundances of light elements based on the big bang nucleosynthesis model are calculated using the Tsallis non-extensive statistics. The impact of the variation of the non-extensive parameter q from the unity value is compared to observations and to the abundance yields from the standard big bang model. We find large differences between the reaction rates and the abundance of light elements calculated with the extensive and the non-extensive statistics. A large deviation of the non-extensive parameter from q=1 (corresponding to Boltzmann statistics) does not seem to be compatible with observations.

Dark Matter Primordial Black Holes and Inflation Models

astro-ph — Fri, 18 May 2012 00:39:33 +0000

A broad range of single field models of inflation are analyzed in light of all relevant recent cosmological data, checking whether they can lead to the formation of long–lived Primordial Black Holes (PBHs) as candidate for dark matter. To that end we calculate the spectral index of the power spectrum of primordial perturbations as well as its first and second derivatives. PBH formation is possible only if the spectral index $n_S(k_0)$ increases significantly at small scales. Since current data indicate that the first derivative $\alpha_S$ of the spectral index is negative at the pivot scale, PBH formation is only possible in the presence of a sizable and positive second derivative (“running of the running”) $\beta_S$. Among the three small-field and five large-field models we analyze, only the “running-mass” model allows PBH formation, for a narrow range of parameters.

Flux and Photon Spectral Index Distributions of Fermi-LAT Blazars And Contribution To The Extragalactic Gamma-ray Background [Replacement]

astro-ph — Fri, 18 May 2012 00:37:36 +0000

We present a determination of the distributions of photon spectral index and gamma-ray flux – the so called LogN-LogS relation – for the 352 blazars detected with a greater than approximately seven sigma detection threshold and located above +/- 20 degrees Galactic latitude by the Large Area Telescope of the Fermi Gamma-ray Space Telescope in its first year catalog. Because the flux detection threshold depends on the photon index, the observed raw distributions do not provide the true LogN-LogS counts or the true distribution of the photon index. We use the non-parametric methods developed by Efron and Petrosian to reconstruct the intrinsic distributions from the observed ones which account for the data truncations introduced by observational bias and includes the effects of the possible correlation between the two variables. We demonstrate the robustness of our procedures using a simulated data set of blazars and then apply these to the real data and find that for the population as a whole the intrinsic flux distribution can be represented by a broken power law with high and low indexes of -2.37 +/- 0.13 and -1.70 +/- 0.26, respectively, and the intrinsic photon index distribution can be represented by a Gaussian with mean of 2.41 +/- 0.13 and width of 0.25 +/- 0.03. We also find the intrinsic distributions for the sub-populations of BL Lac and FSRQs type blazars separately. We then calculate the contribution of Fermi blazars to the diffuse extragalactic gamma-ray background radiation. Under the assumption that the flux distribution of blazars continues to arbitrarily low fluxes, we calculate the best fit contribution of all blazars to the total extragalactic gamma-ray output to be 60%, with a large uncertainty.

Cosmological Sakharov Oscillations and Quantum Mechanics of the Early Universe [Replacement]

astro-ph — Fri, 18 May 2012 00:37:23 +0000

This is a brief summary of a talk delivered at the Special Session of the Physical Sciences Division of the Russian Academy of Sciences, Moscow, 25 May 2011. The meeting was devoted to the 90-th anniversary of A. D. Sakharov. The focus of this contribution is on the standing-wave pattern of quantum-mechanically generated metric (gravitational field) perturbations as the origin of subsequent Sakharov oscillations in the matter power spectrum. Other related phenomena, particularly in the area of gravitational waves, and their observational significance are also discussed.

Panchromatic Observations of SN 2011dh Point to a Compact Progenitor Star [Replacement]

astro-ph — Fri, 18 May 2012 00:37:05 +0000

We report the discovery and detailed monitoring of X-ray emission associated with the Type IIb SN 2011dh using data from the Swift and Chandra satellites, placing it among the best studied X-ray supernovae to date. We further present millimeter and radio data obtained with the SMA, CARMA, and EVLA during the first three weeks after explosion. Combining these observations with early optical photometry, we show that the panchromatic dataset is well-described by non-thermal synchrotron emission (radio/mm) with inverse Compton scattering (X-ray) of a thermal population of optical photons. In this scenario, the shock partition fractions deviate from equipartition by a factor, (e_e/e_B) ~ 30. We derive the properties of the shockwave and the circumstellar environment and find a shock velocity, v~0.1c, and a progenitor mass loss rate of ~6e-5 M_sun/yr. These properties are consistent with the sub-class of Type IIb SNe characterized by compact progenitors (Type cIIb) and dissimilar from those with extended progenitors (Type eIIb). Furthermore, we consider the early optical emission in the context of a cooling envelope model to estimate a progenitor radius of ~1e+11 cm, in line with the expectations for a Type cIIb SN. Together, these diagnostics are difficult to reconcile with the extended radius of the putative yellow supergiant progenitor star identified in archival HST observations, unless the stellar density profile is unusual. Finally, we searched for the high energy shock breakout pulse using X-ray and gamma-ray observations obtained during the purported explosion date range. Based on the compact radius of the progenitor, we estimate that the breakout pulse was detectable with current instruments but likely missed due to their limited temporal/spatial coverage. [Abridged]

Galaxy Zoo: dust and molecular gas in early-type galaxies with prominent dust lanes [Replacement]

astro-ph — Fri, 18 May 2012 00:36:55 +0000

We study dust and associated molecular gas in 352 nearby early-type galaxies (ETGs) with prominent dust lanes. 65% of these `dusty ETGs’ (D-ETGs) are morphologically disturbed, suggesting a merger origin. This is consistent with the D-ETGs residing in lower density environments compared to the controls drawn from the general ETG population. 80% of D-ETGs inhabit the field (compared to 60% of the controls) and <2% inhabit clusters (compared to 10% of the controls). Compared to the controls, D-ETGs exhibit bluer UV-optical colours (indicating enhanced star formation) and an AGN fraction that is more than an order of magnitude greater (indicating higher incidence of nuclear activity). The clumpy dust mass residing in large-scale features is estimated, using the SDSS r-band images, to be 10^{4.5}-10^{6.5} MSun. A comparison to the total (clumpy + diffuse) dust masses- calculated using the far-IR fluxes of 15% of the D-ETGs that are detected by the IRAS- indicates that only ~20% of the dust resides in these large-scale features. The dust masses are several times larger than the maximum value expected from stellar mass loss, ruling out an internal origin. The dust content shows no correlation with the blue luminosity, indicating that it is not related to a galactic scale cooling flow. No correlation is found with the age of the recent starburst, suggesting that the dust is accreted directly in the merger rather than being produced in situ by the triggered star formation. Using molecular gas-to-dust ratios of ETGs in the literature we estimate that the median current and initial molecular gas fraction are ~1.3% and ~4%, respectively. Recent work suggests that the merger activity in nearby ETGs largely involves minor mergers (mass ratios between 1:10 and 1:4). If the IRAS-detected D-ETGs form via this channel, then the original gas fractions of the accreted satellites are 20%-44%. [Abridged]

Galaxy evolution in groups and clusters: star formation rates, red sequence fractions, and the persistent bimodality [Replacement]

astro-ph — Fri, 18 May 2012 00:36:28 +0000

Using galaxy group/cluster catalogs created from the Sloan Digital Sky Survey Data Release 7, we examine in detail the specific star formation rate (SSFR) distribution of satellite galaxies and its dependence on stellar mass, host halo mass, and halo-centric radius. All galaxies, regardless of central-satellite designation, exhibit a similar bimodal SSFR distribution, with a strong break at SSFR ~ 10^-11 yr^-1 and the same high SSFR peak; in no regime is there ever an excess of galaxies in the `green valley’. Satellite galaxies are simply more likely to lie on the quenched (`red sequence’) side of the SSFR distribution. Furthermore, the satellite quenched fraction excess above the field galaxy value is nearly independent of galaxy stellar mass. An enhanced quenched fraction for satellites persists in groups with halo masses down to 3 x 10^11 Msol and increases strongly with halo mass and toward halo center. We find no detectable quenching enhancement for galaxies beyond ~2R_vir around massive clusters once these galaxies have been decomposed into centrals and satellites. These trends imply that (1) galaxies experience no significant environmental effects until they cross within ~R_vir of a more massive host halo, (2) after this, star formation in active satellites continues to evolve in the same manner as active central galaxies for several Gyrs, and (3) once begun, satellite star formation quenching occurs rapidly. These results place strong constraints on satellite-specific quenching mechanisms, as we will discuss further in companion papers.

Kicking massive black holes off clusters: Intermediate-mass ratio inspirals [Replacement]

astro-ph — Fri, 18 May 2012 00:35:33 +0000

Contrary to supermassive and stellar-mass black holes (SBHs), the existence of intermediate-mass black holes (IMBHs) with masses ranging between 100 and 10,000 Msun has not yet been confirmed. The main problem in the detection is that the innermost stellar kinematics of globular clusters (GCs), the natural loci to IMBHs, are very difficult to resolve. However, if IMBHs reside in the center of GCs, a possibility is that they interact dynamically with their enviroment. A binary formed with the IMBH and a compact object of the GC would naturally lead to a prominent source of gravitational radiation, detectable with future observatories. We run for the first time direct-summation integrations of GCs with an IMBH including the dynamical evolution of the IMBH with the stellar system and relativistic effects, such as energy loss in gravitational waves (GWs) and periapsis shift, and gravitational recoil. We find in one of our models an intermediate-mass ratio inspiral (IMRI), which leads to a merger with a recoiling velocity higher than the escape velocity of the GC. The GWs emitted fall in the range of frequencies that a LISA-like observatory could detect, like the European eLISA or in mission options considered in the recent preliminary mission study conducted in China. The merger has an impact on the global dynamics of the cluster, as an important heating source is removed when the merged system leaves the GC. The detection of one IMRI would constitute a test of GR, as well as an irrefutable proof of the existence of IMBHs.

Multiphase, non-spherical gas accretion onto a black hole [Replacement]

astro-ph — Fri, 18 May 2012 00:34:46 +0000

(Abridged) We investigate non-spherical behavior of gas accreting onto a central supermassive black hole performing simulations using the SPH code GADGET-3 including radiative cooling and heating by the central X-ray source. As found in earlier 1D studies, our 3D simulations show that the accretion mode depends on the X-ray luminosity (L_X) for a fixed density at infinity and accretion efficiency. In the low L_X limit, gas accretes in a stable, spherically symmetric fashion. In the high L_X limit, the inner gas is significantly heated up and expands, reducing the central mass inflow rate. The expanding gas can turn into a strong enough outflow capable of expelling most of the gas at larger radii. For some intermediate L_X, the accretion flow becomes unstable developing prominent non-spherical features, the key reason for which is thermal instability (TI) as shown by our analyses. Small perturbations of the initially spherically symmetric accretion flow that is heated by the intermediate L_X quickly grow to form cold and dense clumps surrounded by overheated low density regions. The cold clumps continue their inward motion forming filamentary structures; while the hot infalling gas slows down because of buoyancy and can even start outflowing through the channels in between the filaments. We found that the ratio between the mass inflow rates of the cold and hot gas is a dynamical quantity depending on several factors: time, spatial location, and L_X; and ranges between 0 and 4. We briefly discuss astrophysical implications of such TI-driven fragmentation of accreting gas on the formation of clouds in narrow and broad line regions of AGN, the formation of stars, and the observed variability of the AGN luminiosity.

Approximate Bayesian Computation for Astronomical Model Analysis: A Case Study in Galaxy Demographics and Morphological Transformation at High Redshift [Replacement]

astro-ph — Fri, 18 May 2012 00:34:08 +0000

“Approximate Bayesian Computation” (ABC) represents a powerful methodology for the analysis of complex stochastic systems for which the likelihood of the observed data under an arbitrary set of input parameters may be entirely intractable-the latter condition rendering useless the standard machinery of tractable likelihood-based, Bayesian statistical inference (e.g. conventional Markov Chain Monte Carlo simulation; MCMC). In this article we demonstrate the potential of ABC for astronomical model analysis by application to a case study in the morphological transformation of high redshift galaxies. To this end we develop, first, a stochastic model for the competing processes of merging and secular evolution in the early Universe; and second, through an ABC-based comparison against the observed demographics of massive (M_gal > 10^11 M_sun) galaxies (at 1.5 < z < 3) in the CANDELS/EGS dataset we derive posterior probability densities for the key parameters of this model. The "Sequential Monte Carlo" (SMC) implementation of ABC exhibited herein, featuring both a self-generating target sequence and self-refining MCMC kernel, is amongst the most efficient of contemporary approaches to this important statistical algorithm. We highlight as well through our chosen case study the value of careful summary statistic selection, and demonstrate two modern strategies for assessment and optimisation in this regard. Ultimately, our ABC analysis of the high redshift morphological mix returns tight constraints on the evolving merger rate in the early Universe and favours major merging (with disc survival or rapid reformation) over secular evolution as the mechanism most responsible for building up the first generation of bulges in early-type disks.

The Shift of the Baryon Acoustic Oscillation Scale: A Simple Physical Picture [Replacement]

astro-ph — Fri, 18 May 2012 00:33:29 +0000

A shift of the baryon acoustic oscillation (BAO) scale to smaller values than predicted by linear theory was observed in simulations. In this paper, we try to provide an intuitive physical understanding of why this shift occurs, explaining in more pedagogical detail earlier perturbation theory calculations. We find that the shift is mainly due to the following physical effect. A measurement of the BAO scale is more sensitive to regions with long wavelength overdensities than underdensities, because (due to non-linear growth and bias) these overdense regions contain larger fluctuations and more tracers and hence contribute more to the total correlation function. In overdense regions the BAO scale shrinks because such regions locally behave as positively curved closed universes, and hence a smaller scale than predicted by linear theory is measured in the total correlation function. Other effects which also contribute to the shift are briefly discussed. We provide approximate analytic expressions for the non-linear shift including a brief discussion of biased tracers and explain why reconstruction should entirely reverse the shift. Our expressions and findings are in agreement with simulation results, and confirm that non-linear shifts should not be problematic for next-generation BAO measurements.

Very small-scale clustering of quasars from a complete quasar lens survey [Replacement]

astro-ph — Fri, 18 May 2012 00:33:10 +0000

We measure the small-scale (comoving separation 10 kpc/h < r_p < 200 kpc/h) two-point correlation function of quasars using a sample of 26 spectroscopically confirmed binary quasars at 0.6

Gauge-invariant variables in general-relativistic perturbations: globalization and zero-mode problem [Replacement]

astro-ph — Fri, 18 May 2012 00:32:59 +0000

An outline of a proof of the local decomposition of linear metric perturbations into gauge-invariant and gauge-variant parts on an arbitrary background spacetime is briefly explained. We explicitly construct the gauge-invariant and gauge-variant parts of the linear metric perturbations based on some assumptions. We also point out the zero-mode problem is an essential problem to globalize of this decomposition of linear metric perturbations. The resolution of this zero-mode problem implies the possibility of the development of the higher-order gauge-invariant perturbation theory on an arbitrary background spacetime in a global sense.

Dark matter origin of the gamma ray emission from the galactic center observed by HESS [Replacement]

astro-ph — Fri, 18 May 2012 00:32:37 +0000

We show that the gamma ray spectrum observed with the HESS array of Cherenkov telescopes coming from the Galactic Center (GC) region and identified with the source HESS J1745-290, is well fitted by the secondary photons coming from dark matter (DM) annihilation over a diffuse power-law background. The amount of photons and morphology of the signal localized within a region of few parsecs, require compressed DM profiles as those resulting from baryonic contraction, which offer $\sim 10^3$ enhancements in the signal over DM alone simulations. The fitted background from HESS data is consistent with recent Fermi-LAT observations of the same region.

EzGal: A Flexible Interface for Stellar Population Synthesis Models [Replacement]

astro-ph — Fri, 18 May 2012 00:32:13 +0000

We present EzGal, a flexible python program designed to easily generate observable parameters (magnitudes, colors, mass-to-light ratios) for any stellar population synthesis (SPS) model. As has been demonstrated by various authors, the choice of input SPS models can be a significant source of systematic uncertainty. A key strength of EzGal is that it enables simple, direct comparison of different models sets. EzGal is also capable of generating composite stellar population models (CSPs) and can interpolate between metallicities for a given model set. We have created a web interface to run EzGal and generate observables for a variety of star formation histories and model sets. We make many commonly used SPS models available from this interface; the BC03 models, an updated version of these models, the Maraston models, the BaSTI models, and finally the FSPS models. We use EzGal to compare magnitude predictions for the model sets as a function of wavelength, age, metallicity, and star formation history. We recover the well-known result that the models agree best in the optical for old, solar metallicity models, with differences at the ~0.1 magnitude level. The most problematic regime for SPS modeling is for young ages (7500 Angstroms) where scatter between models can vary from 0.3 mags (Sloan i) to 0.7 mags (Ks). We find that these differences are best understood as general uncertainties in SPS modeling. Finally we explore a more physically motivated example by generating CSPs with a star formation history matching the global star formation history of the universe. We demonstrate that the wavelength and age dependence of SPS model uncertainty translates into a redshift dependent model uncertainty, highlighting the importance of a quantitative understanding of model differences when comparing observations to models as a function of redshift.

Precision Measurement of The Most Distant Spectroscopically Confirmed Supernova Ia with the Hubble Space Telescope [Replacement]

astro-ph — Fri, 18 May 2012 00:31:06 +0000

We report the discovery of a redshift 1.71 supernova in the GOODS North field. The Hubble Space Telescope (HST) ACS spectrum has almost negligible contamination from the host or neighboring galaxies, allowing us to confirm it as a Type Ia. A recent serendipitous archival HST WFC3 grism spectrum contributed a key element of the confirmation by giving a host-galaxy redshift of 1.713 +/- 0.007, matching the SN redshift. In addition to being the most distant SN Ia with spectroscopic confirmation, this is the most distant Ia with a precision color measurement. We present the ACS WFC and NICMOS 2 photometry and ACS and WFC3 spectroscopy. Our derived supernova distance is in agreement with the prediction of LambdaCDM.

The optically unbiased GRB host (TOUGH) survey. III. Redshift distribution

astro-ph — Thu, 17 May 2012 00:58:08 +0000

We present 10 new gamma-ray burst (GRB) redshifts and another five redshift limits based on host galaxy spectroscopy obtained as part of a large program conducted at the Very Large Telescope (VLT). The redshifts span the range 0.345 < z 6 (z > 7). The mean redshift of the host sample is assessed to be > 2.2, with the 10 new redshifts reducing it significantly. Using this more complete sample, we confirm previous findings that the GRB rate at high redshift (z > 3) appears to be in excess of predictions based on assumptions that it should follow conventional determinations of the star formation history of the universe, combined with an estimate of its likely metallicity dependence. This suggests that either star formation at high redshifts has been significantly underestimated, for example due to a dominant contribution from faint, undetected galaxies, or that GRB production is enhanced in the conditions of early star formation, beyond that usually ascribed to lower metallicity.

Extending BEAMS to correlated photometric supernova data

astro-ph — Thu, 17 May 2012 00:57:05 +0000

New supernova surveys such as the Dark Energy Survey, Pan-STARRS and the LSST will produce an unprecedented number of photometric supernova candidates, most with no spectroscopic follow-up. Avoiding biases in cosmological parameters due to the resulting inevitable contamination from non-Ia supernovae can be achieved with the BEAMS formalism, allowing the first fully photometric supernova cosmology studies. Here we extend BEAMS to deal with the case in which the supernovae are correlated. Doing this analytically requires evaluating 2^N terms in the posterior, where N is the number of supernova candidates. This `exponential catastrophe’ is computationally unfeasible even for N of order 100. We circumvent the exponential catastrophe by marginalising numerically instead of analytically over the possible supernovae types: we augment the cosmological parameters with N discrete type parameters, tau_i, that we include in our MCMC analysis. We show that this deals well even with large correlations without a major increase in computational time, whereas ignoring the correlations can lead to significant biases. We then compare the numerical marginalisation technique with a perturbative expansion of the posterior based on the insight that future surveys will have exquisite light curves and hence the probability that a given candidate is a Type Ia will be close to unity or zero, for most objects. Although this perturbative approach changes computation of the posterior from a 2^N problem into an N^2 or N^3 one, we show that it leads to biases in general through a small number of misclassifications, implying that numerical marginalisation is superior.

Precision Measurement of The Most Distant Spectroscopically-Confirmed Supernova Ia with the Hubble Space Telescope

astro-ph — Thu, 17 May 2012 00:56:48 +0000

We report the discovery of a redshift 1.71 supernova in the GOODS North field. The Hubble Space Telescope (HST) ACS spectrum has almost negligible contamination from the host or neighboring galaxies, allowing us to confirm it as a Type Ia. A serendipitous HST WFC3 IR spectrum, taken after the supernova had faded, gives a host-galaxy redshift of 1.713 +/- 0.007 which matches the SN redshift. In addition to being the most distant SN Ia with spectroscopic confirmation, this is the most distant Ia with a precision color measurement. We present the ACS WFC and NICMOS 2 photometry and ACS and WFC3 spectroscopy. Our derived supernova distance is in agreement with the prediction of LambdaCDM.

Runaway Stars and the Escape of Ionizing Radiation from High-Redshift Galaxies

astro-ph — Thu, 17 May 2012 00:56:15 +0000

Approximately 30% of all massive stars in the Galaxy are runaways with velocities exceeding 30 km/s. Their high speeds allow them to travel ~0.1-1 kpc away from their birth place before they explode at the end of their several Myr lifetimes. At high redshift, when galaxies were much smaller than in the local universe, runaways could venture far from the dense inner regions of their host galaxies. From these large radii, and therefore low column densities, much of their ionizing radiation is able to escape into the intergalactic medium. Runaways may therefore significantly enhance the overall escape fraction of ionizing radiation, fesc, from small galaxies at high redshift. We present simple models of the high-redshift runaway population and its impact on fesc as a function of halo mass, size, and redshift. We find that the inclusion of runaways enhances fesc by factors of ~1.1-8, depending on halo mass, galaxy geometry, and the mechanism of runaway production, implying that runaways may contribute 50-90% of the total ionizing radiation escaping from high-redshift galaxies. Runaways may therefore play an important role in reionizing the universe.

[CII] line emission in massive star-forming galaxies at z=4.7

astro-ph — Thu, 17 May 2012 00:55:55 +0000

We present Atacama Large Millimeter/submillimeter Array (ALMA) observations of the [CII] 157.7micron fine structure line and thermal dust continuum emission from a pair of gas-rich galaxies at z=4.7, BR1202-0725. This system consists of a luminous quasar host galaxy and a bright submm galaxy (SMG), while a fainter star-forming galaxy is also spatially coincident within a 4” (25 kpc) region. All three galaxies are detected in the submm continuum, indicating FIR luminosities in excess of 10^13 Lsun for the two most luminous objects. The SMG and the quasar host galaxy are both detected in [CII] line emission with luminosities, L([CII]) = (10.0 +/- 1.5)x10^9 Lsun and L([CII]) = (6.5+/-1.0)x10^9 Lsun, respectively. We estimate a luminosity ratio, L([CII])/L(FIR) = (8.3+/-1.2)x10^-4 for the starburst SMG to the North, and L([CII])/L(FIR) = (2.5+/-0.4)x10^-4 for the quasar host galaxy, in agreement with previous high-redshift studies that suggest lower [CII]-to-FIR luminosity ratios in quasars than in starburst galaxies. The third fainter object with a flux density, S(340GHz) = 1.9+/-0.3 mJy, is coincident with a Ly-Alpha emitter and is detected in HST ACS F775W and F814W images but has no clear counterpart in the H-band. Even if this third companion does not lie at a similar redshift to BR1202-0725, the quasar and the SMG represent an overdensity of massive, infrared luminous star-forming galaxies within 1.3 Gyr of the Big Bang.

Electron-positron plasma in GRBs and in cosmology

astro-ph — Thu, 17 May 2012 00:53:57 +0000

Electron-positron plasma is believed to play imporant role both in the early Universe and in sources of Gamma-Ray Bursts (GRBs). We focus on analogy and difference between physical conditions of electron-positron plasma in the early Universe and in sources of GRBs. We discuss a) dynamical differences, namely thermal acceleration of the outflow in GRB sources vs cosmological deceleration; b) nuclear composition differences as synthesis of light elements in the early Universe and possible destruction of heavy elements in GRB plasma; c) different physical conditions during last scattering of photons by electrons. Only during the acceleration phase of the optically thick electron-positron plasma comoving observer may find it similar to the early Universe. This similarity breaks down during the coasting phase. Reprocessing of nuclear abundances may likely take place in GRB sources. Heavy nuclear elements are then destroyed, resulting mainly in protons with small admixture of helium. Unlike the primordial plasma which recombines to form neutral hydrogen, and emits the Cosmic Microwave Background Radiation, GRB plasma does not cool down enough to recombine.

The `harder when brighter’ X-ray behaviour of the low luminosity active galactic nucleus NGC 7213

astro-ph — Thu, 17 May 2012 00:53:43 +0000

We present the first robust evidence of an anti-correlation between the X-ray photon index, \Gamma, and the X-ray luminosity in a single low luminosity active galactic nuclei (LLAGN), NGC 7213. Up to now, such anti-correlation trends have been seen only in large samples of LLAGN that span a wide range of X-ray fluxes, although the opposite behaviour (i.e. a positive correlation between \Gamma and X-ray luminosity) has been extensively studied for individual X-ray bright active galactic nuclei. For NGC 7213, we use the long-term X-ray monitoring data of Rossi X-ray Timing Explorer (RXTE), regularly obtained on average every two days from March 2006 to December 2009. Based on our X-ray data, we derive the \Gamma versus flux and the hardness ratio versus flux relations, indicating clearly that NGC 7213 follows a `harder when brighter’ spectral behaviour. Additionally, by analysing radio and optical data, and combining data from the literature, we form the most complete spectral energy distribution (SED) of the source across the electromagnetic spectrum yielding a bolometric luminosity of 1.7*10^43 erg s^-1. Phenomenologically, the SED of NGC 7213 is similar to that of low-ionization nuclear emission-line region. The robust anti-correlation trend that we find between \Gamma and X-ray luminosity together with the low accretion rate of the source, 0.14 per cent that of Eddington limit, make NGC 7213 the first LLAGN exhibiting a similar spectral behaviour with that of black hole X-ray binaries in `hard state’.

Discovery of the most isolated globular cluster in the local universe

astro-ph — Thu, 17 May 2012 00:52:07 +0000

We report the discovery of two new globular clusters in the remote halos of M81 and M82 in the M81 Group based on Hubble Space Telescope archive images. They are brighter than typical globular clusters (MV = -9.34 mag for GC-1 and M_V = -10.51 mag for GC-2), and much larger than known globular clusters with similar luminosity in the MilkyWay Galaxy and M81. Radial surface brightness profiles for GC-1 and GC-2 do not show any features of tidal truncation in the outer part. They are located much farther from both M81 and M82 in the sky, compared with previously known star clusters in these galaxies. Color-magnitude diagrams of resolved stars in each cluster show a well-defined red giant branch (RGB), indicating that they are metal-poor and old. We derive a low metallicity with [Fe/H] $\simeq -2.3$ and an old age ~14 Gyr for GC-2 from the analysis of the absorption lines in its spectrum in the Sloan Digital Sky Survey in comparison with the simple stellar population models. The I-band magnitude of the tip of the RGB for GC-2 is 0.26 mag fainter than that for the halo stars in the same field, showing that GC-2 is ~400 kpc behind the M81 halo along our line of sight. The deprojected distance to GC-2 from M81 is much larger than any other known globular clusters in the local universe. This shows that GC-2 is the most isolated globular cluster in the local universe.

Heating the intra-cluster medium perpendicular to the jets axis

astro-ph — Thu, 17 May 2012 00:51:06 +0000

By simulating jet-inflated bubbles in cooling flows with the PLUTO hydrodynamic code we show that mixing of high entropy shocked jet’s material with the intra-cluster medium (ICM) is the major heating process perpendicular to the jets’ axis. Heating by the forward shock is not significant. The mixing is very efficient in heating the ICM in all directions, to distances of ~10kpc and more. Although the jets are active for a time period of only 20 Myr, the mixing and heating near the equatorial plane, as well as along the symmetry axis, continues to counter radiative cooling for times of >10^8 yr after the jets have ceased to exist. We discuss some possible implications of the results. (i) The vigorous mixing is expected to entangle magnetic field lines, hence to suppress any global heat conduction in the ICM near the center. (ii) The vigorous mixing forms multi-phase ICM in the inner cluster regions, where the coolest parcels of gas will eventually cool first, flow inward, and feed the active galactic nucleus to set the next jet-activity episode. This further supports the cold feedback mechanism. (iii) In cases where the medium outside the region of r~10kpc is not as dense as in groups and clusters of galaxies, like during the process of galaxy formation, the forward shock and the high pressure of the shocked jets’ material might expel gas from the system.

Lepton asymmetries and primordial hypermagnetic helicity evolution

astro-ph — Thu, 17 May 2012 00:50:04 +0000

The hypermagnetic helicity density at the electroweak phase transition (EWPT) exceeds many orders of magnitude the galactic magnetic helicity density. Together with previous magnetic helicity evolution calculations after the EWPT and hypermagnetic helicity conversion to the magnetic one at the EWPT, the present calculation completes the description of the evolution of this important topological feature of cosmological magnetic fields. It suggests that if the magnetic field seeding the galactic dynamo has a primordial origin, it should be substantially helical. This should be taken into account in scenarios of galactic magnetic field evolution with a cosmological seed.

Effective field theory for perturbations in dark energy and modified gravity

astro-ph — Thu, 17 May 2012 00:49:40 +0000

When recent observational evidence and the GR+FRW+CDM model are combined we obtain the result that the Universe is accelerating, where the acceleration is due to some not-yet-understood “dark sector”. There has been a considerable number of theoretical models constructed in an attempt to provide an “understanding” of the dark sector: dark energy and modified gravity theories. The proliferation of modified gravity and dark energy models has brought to light the need to construct a “generic” way to parameterize the dark sector. We will discuss our new way of approaching this problem. We write down an effective action for linearized perturbations to the gravitational field equations for a given field content; crucially, our formalism does not require a Lagrangian to be presented for calculations to be performed and observational predictions to be extracted. Our approach is inspired by that taken in particle physics, where the most general modifications to the standard model are written down for a given field content that is compatible with some assumed symmetry (which we take to be isotropy of the background spatial sections).

Satellites around massive galaxies since z$\sim$2: confronting the Millennium simulation with observations

astro-ph — Thu, 17 May 2012 00:49:22 +0000

Minor merging has been postulated as the most likely evolutionary path to produce the increase in size and mass observed in the massive galaxies since z$\sim$2. In this Letter, we test directly this hypothesis comparing the population of satellites around massive galaxies in cosmological simulations versus the observations. We use state-of-the-art, publically available, Millennium I and II simulations and the associated semi-analytical galaxy catalogues to explore the time evolution of the fraction of massive galaxies that have satellites, the number of satellites per galaxy, the projected distance at which the satellite locate from the host galaxy, and the mass ratio between the host galaxies and their satellites. The three virtual galaxy catalogues considered here, overproduce the fraction of galaxies with satellites by a factor ranging between 1.5 and 6 depending on the epoch, whereas the mean projected distance and ratio of the satellite mass over host mass are in closer agreement with data. The larger pull of satellites in the semi-analytical samples could suggest that the size evolution found in previous hydrodynamical simulations is an artifact due to the larger number of infalling satellites compared to the real Universe. These results advise to revise the physical ingredients implemented in the semi-analytical models in order to reconcile the observed and computed fraction of galaxies with satellites, and eventually, it would leave some room to other mechanisms explaining the galaxy size growth not related to the minor merging.

AGN and Megamasers

astro-ph — Thu, 17 May 2012 00:48:28 +0000

Luminous extragalactic masers are traditionally referred to as the `megamasers’. Those produced by water molecules are associated with accretion disks, radio jets, or outflows in the nuclear regions of active galactic nuclei (AGN). The majority of OH maser sources are instead driven by intense star formation in ultra-luminous infrared galaxies, although in a few cases the OH maser emission traces rotating (toroidal or disk) structures around the nuclear engines of AGN. Thus, detailed maser studies provide a fundamental contribution to our knowledge of the main nuclear components of AGN, constitute unique tools to measure geometric distances of host galaxies, and have a great impact on probing the, so far, paradigmatic Unified Model of AGN.

Mass and pressure constraints on galaxy clusters from interferometric SZ observations

astro-ph — Thu, 17 May 2012 00:47:55 +0000

Following on our previous study of an analytic parametric model to describe the baryonic and dark matter distributions in clusters of galaxies with spherical symmetry, we perform an SZ analysis of a set of simulated clusters and present their mass and pressure profiles. The simulated clusters span a wide range in mass, 2.0 x 10^14 Msun < M200 < 1.0 x 10^15Msun, and observations with the Arcminute Microkelvin Imager (AMI) are simulated through their Sunyaev- Zel'dovich (SZ) effect. We assume that the dark matter density follows a Navarro, Frenk and White (NFW) profile and that the gas pressure is described by a generalised NFW (GNFW) profile. By numerically exploring the probability distributions of the cluster parameters given simulated interferometric SZ data in the context of Bayesian methods, we investigate the capability of this model and analysis technique to return the simulated clusters input quantities. We show that considering the mass and redshift dependency of the cluster halo concentration parameter is crucial in obtaining an unbiased cluster mass estimate and hence deriving the radial profiles of the enclosed total mass and the gas pressure out to r200.

Inflating a chain of x-ray deficient bubbles by a single jet activity episode

astro-ph — Thu, 17 May 2012 00:46:46 +0000

We show that a continuous jet with time-independent launching properties can inflate a chain of close and overlapping X-ray deficient bubbles. Using the numerical code PLUTO we run 2.5D hydrodynamic simulations and study the interaction of the jets with the intra-cluster medium (ICM). A key process is vortex fragmentation due to several mechanisms, including vortex-shedding and Kelvin-Helmholtz (KH) instabilities. Our results can account for the structure of two opposite chains of close bubbles as observed in the galaxy cluster Hydra A and galaxy group NGC 5813. Our results imply that the presence of multiple pairs of bubbles does not necessarily imply several jet-launching episodes. This finding might have implications to feedback mechanisms operating by jets.

Circumnuclear star-forming regions in early type spiral galaxies: dynamical masses

astro-ph — Thu, 17 May 2012 00:44:41 +0000

We present the measurements of gas and stellar velocity dispersions in 17 circumnuclear star-forming regions (CNSFRs) and the nuclei of three barred spiral galaxies: NGC2903, NGC3310 and NGC3351 from high dispersion spectra. The stellar dispersions have been obtained from the CaII triplet (CaT) lines at 8494, 8542, 8662A, while the gas velocity dispersions have been measured by Gaussian fits to the Hbeta and to the [OIII]5007A\ lines. The CNSFRs, with sizes of about 100 to 150pc in diameter, are seen to be composed of several individual star clusters with sizes between 1.5 and 6.2pc on HST images. Using the stellar velocity dispersions, we have derived dynamical masses for the entire star-forming complexes and for the individual star clusters. Values of the stellar velocity dispersions are between 31 and 73 km/s. Dynamical masses for the whole CNSFRs are between 4.9×10^6 and 1.9×10^8 Mo and between 1.4×10^6 and 1.1×10^7 Mo for the individual star clusters. We have found indications for the presence of two different kinematical components in the ionized gas of the regions. The narrow component of the two-component Gaussian fits seem to have a relatively constant value for all the studied CNSFRs, with estimated values close to 25 km/s. This narrow component could be identified with ionized gas in a rotating disc, while the stars and the fraction of the gas (responsible for the broad component) related to the star-forming regions would be mostly supported by dynamical pressure.

Dark energy from a renormalization group flow

astro-ph — Thu, 17 May 2012 00:44:28 +0000

We present evidence that a special class of gravitationally-coupled hidden sectors, in which conformal invariance is dynamically broken in a controlled way, exhibit the properties of dark energy. Such quantum field theories may appear while embedding the Standard Model in a more fundamental high energy theory. At late times, an effective dark energy field behaves similarly to an exponentially small cosmological constant while at early times its energy density partly tracks that of matter.

Spontaneous symmetry breaking in inflationary cosmology: on the fate of Goldstone Bosons

astro-ph — Thu, 17 May 2012 00:41:11 +0000

We argue that in an inflationary cosmology a consequence of the lack of time translational invariance is that spontaneous breaking of a continuous symmetry and Goldstone’s theorem \emph{do not} imply the existence of \emph{massless} Goldstone modes. We study spontaneous symmetry breaking in an O(2) model, and implications for O(N) in de Sitter space time. The Goldstone mode acquires a radiatively generated mass as a consequence of infrared divergences, and the continuous symmetry is spontaneously broken for any finite $N$, however there is a \emph{first order phase transition} as a function of the Hawking temperature $T_H=H/2\pi$. For O(2) the symmetry is spontaneously broken for $T_H < T_c= \lambda^{1/4} v/2.419$ where $\lambda$ is the quartic coupling and $v$ is the tree level vacuum expectation value and the Goldstone mode acquires a radiatively generated mass $\mathcal{M}^2_\pi \propto \lambda^{1/4} H$. The first order nature of the transition is a consequence of the strong infrared behavior of minimally coupled scalar fields in de Sitter space time, the jump in the order parameter at $T_H=T_c$ is $\sigma_{0c} \simeq 0.61\, {H}/{\lambda^{1/4}}$. In the strict $N\rightarrow \infty$ the symmetry cannot be spontaneously broken. Furthermore, the lack of kinematic thresholds imply that the Goldstone modes \emph{decay} into Goldstone and Higgs modes by emission and absorption of superhorizon quanta.

Constraints on variation in $\alpha$ and $m_e$ from WMAP 7-year data [Replacement]

astro-ph — Thu, 17 May 2012 00:40:37 +0000

We update the constraints on the time variation of the fine structure constant $\alpha$ and the electron mass $m_e$, using the latest CMB data, including the 7-yr release of WMAP. We made statistical analyses of the variation of each one of the constants and of their joint variation, together with the basic set of cosmological parameters. We used a modified version of CAMB and COSMOMC to account for these possible variations. We present bounds on the variation of the constants for different data sets, and show how results depend on them. When using the latest CMB data plus the power spectrum from Sloan Digital Sky Survey LRG, we find that $\alpha / \alpha_0=0.986 \pm 0.007$ at 1-$\sigma$ level, when the 6 basic cosmological parameters were fitted, and only variation in $\alpha$ was allowed. The constraints in the case of variation in both constants are $ \alpha / \alpha_0= 0.986 \pm 0.009$ and $m_e / m_{e0} = 0.999 \pm 0.035$. In the case of only variation in $m_e$, the bound is $m_e /m_{e0}=0.964 \pm 0.025$.

Measuring Gravitational Lensing Flexions in Abell 1689 Using an Analytic Image Model [Replacement]

astro-ph — Thu, 17 May 2012 00:40:18 +0000

Measuring dark matter substructure within galaxy cluster haloes is a fundamental probe of the Lambda-CDM model of structure formation. Gravitational lensing is a technique for measuring the total mass distribution which is independent of the nature of the gravitating matter, making it a vital tool for studying these dark-matter dominated objects. We present a new method for measuring weak gravitational lensing flexions, the gradients of the lensing shear field, to measure mass distributions on small angular scales. While previously published methods for measuring flexions focus on measuring derived properties of the lensed images, such as shapelet coefficients or surface brightness moments, our method instead fits a mass-sheet-transformation-invariant Analytic Image Model (AIM) to the each galaxy image. This simple parametric model traces the distortion of lensed image isophotes and constrains the flexion fields. We test the AIM method using simulated data images with realistic noise and a variety of unlensed image properties, and show that it successfully reproduces the input flexion fields. We also apply the AIM method for flexion measurement to Hubble Space Telescope observations of Abell 1689, and detect mass structure in the cluster using flexions measured with the AIM method.

What turns galaxies off? The different morphologies of star-forming and quiescent galaxies since z~2 from CANDELS [Replacement]

astro-ph — Thu, 17 May 2012 00:39:43 +0000

We use HST/WFC3 imaging from the CANDELS Multicycle Treasury Survey, in conjunction with the Sloan Digital Sky Survey, to explore the evolution of galactic structure for galaxies with stellar masses >3e10M_sun from z=2.2 to the present epoch, a time span of 10Gyr. We explore the relationship between rest-frame optical color, stellar mass, star formation activity and galaxy structure. We confirm the dramatic increase from z=2.2 to the present day in the number density of non-star-forming galaxies above 3e10M_sun reported by others. We further find that the vast majority of these quiescent systems have concentrated light profiles, as parametrized by the Sersic index, and the population of concentrated galaxies grows similarly rapidly. We examine the joint distribution of star formation activity, Sersic index, stellar mass, inferred velocity dispersion, and stellar surface density. Quiescence correlates poorly with stellar mass at all z1.3, and somewhat less well at lower redshifts. Yet, there is significant scatter between quiescence and galaxy structure: while the vast majority of quiescent galaxies have prominent bulges, many of them have significant disks, and a number of bulge-dominated galaxies have significant star formation. Noting the rarity of quiescent galaxies without prominent bulges, we argue that a prominent bulge (and perhaps, by association, a supermassive black hole) is an important condition for quenching star formation on galactic scales over the last 10Gyr, in qualitative agreement with the AGN feedback paradigm.

Cosmological constraints on non-standard inflationary quantum collapse models [Replacement]

astro-ph — Thu, 17 May 2012 00:39:02 +0000

We briefly review an important shortcoming –unearthed in previous works– of the standard version of the inflationary model for the emergence of the seeds of cosmic structure. We consider here some consequences emerging from a proposal inspired on ideas of Penrose and Di\’osi about a quantum-gravity induced reduction of the wave function, which has been put forward to address the shortcomings, arguing that its effect on the inflaton field is what can lead to the emergence of the seeds of cosmic structure. The proposal leads to a deviation of the primordial spectrum from the scale-invariant Harrison-Zel’dovich one, and consequently, to a different CMB power spectrum. We perform statistical analyses to test two quantum collapse schemes with recent data from the CMB, including the 7-yr release of WMAP and the matter power spectrum measured using LRGs by the Sloan Digital Sky Survey. Results from the statistical analyses indicate that several collapse models are compatible with CMB and LRG data, and establish constraints on the free parameters of the models. The data put no restriction on the timescale for the collapse of the scalar field modes.

Local P Violation Effects and Thermalization in QCD: Views from Quantum Field Theory and Holography [Replacement]

astro-ph — Thu, 17 May 2012 00:38:12 +0000

We argue that the local violation of P and CP invariance in heavy ion collisions and the universal thermal aspects observed in high energy collisions are in fact two sides of the same coin, and both are related to quantum anomalies of QCD. We argue that the low energy relations representing the quantum anomalies of QCD are saturated by coherent low dimensional vacuum configurations as observed in Monte Carlo lattice studies. The thermal spectrum and approximate universality of the temperature with no dependence on energy of colliding particles in this framework is due to the fact that the emission results from the distortion of these low dimensional vacuum sheets rather than from the colliding particles themselves. The emergence of the long- range correlations of P odd domains (a feature which is apparently required for explanation of the asymmetry observed at RHIC and LHC) is also a result of the same distortion of the QCD vacuum configurations. We formulate the corresponding physics using the effective low energy effective Lagrangian. We also formulate the same physics in terms of the dual holographic picture when low-dimensional sheets of topological charge embedded in 4d space, as observed in Monte Carlo simulations, are identified with D2 branes. Finally, we argue that study of these long range correlations in heavy ion collisions could serve as a perfect test of a proposal that the observed dark energy in present epoch is a result of a tiny deviation of the QCD vacuum energy in expanding universe from its conventional value in Minkowski spacetime.

Ekpyrotic universes in $F(R)$ Ho\v{r}ava-Lifshitz gravity [Replacement]

astro-ph — Thu, 17 May 2012 00:37:36 +0000

The Ekpyrotic scenario is studied in the context of some extensions of Ho\v{r}ava-Lifshitz gravity. Some particular solutions that lead to cyclic Hubble parameters are analyzed, where the corresponding gravitational actions are reconstructed by using several techniques and auxiliary fields. Its comparison with standard $F(R)$ gravity is performed. In addition, the so-called Little Rip, a stage of the universe evolution when some bounded systems may be dissolute, is also studied in this frame of theories.

Observing the first galaxies [Replacement]

astro-ph — Thu, 17 May 2012 00:33:06 +0000

I endeavour to provide a thorough overview of our current knowledge of high-redshift galaxies and their evolution during the first billion years of cosmic time, corresponding to redshifts z > 5. After first summarizing progress with the seven different techniques which have been used to date in the discovery of objects at z > 5, I focus thereafter on the two selection methods which have yielded substantial samples of galaxies at early times, namely Lyman-break and Lyman-alpha selection. I discuss a decade of progress in galaxy sample selection at z ~ 5 – 8, including issues of completeness and contamination, and address some of the confusion which has been created by erroneous reports of extreme-redshift objects. Next I provide an overview of our current knowledge of the evolving ultraviolet continuum and Lyman-alpha galaxy luminosity functions at z ~ 5 – 8, and discuss what can be learned from exploring the relationship between the Lyman-break and Lyman-alpha selected populations. I then summarize what is known about the physical properties of these galaxies in the young universe, before considering the wider implications of this work for the cosmic history of star formation, and for the reionization of the universe. I conclude with a brief summary of the exciting prospects for further progress in this field in the next 5-10 years. Throughout, key concepts such as selection techniques and luminosity functions are explained assuming essentially no prior knowledge. The intention is that this chapter can be used as an introduction to the observational study of high-redshift galaxies, as well as providing a review of the latest results in this fast-moving research field up to the end of 2011.

Massive gravity from bimetric gravity [Replacement]

astro-ph — Thu, 17 May 2012 00:32:25 +0000

We discuss the subtle relationship between so-called massive gravity (that is, gravity incorporating a non-zero graviton mass) and bimetric gravity, focussing particularly on the manner in which massive gravity may be viewed as a suitable limit of bimetric gravity. The limiting procedure is more delicate than currently appreciated, and in particular, in a cosmological context can lead to an interesting interplay between the “background” and “foreground” metrics. The fact that in bimetric theories one always has two sets of metric equations of motion, one for each metric, continues to have an effect even in the massive gravity limit. Thus, solutions of bimetric gravity in the limit of vanishing kinetic term are also solutions of massive gravity, but the contrary statement is not necessarily true.

Gamma-Ray Bursts are precise distance indicators similar to Type Ia Supernovae? [Replacement]

astro-ph — Thu, 17 May 2012 00:32:16 +0000

We estimate the distance modulus to long gamma-ray bursts (LGRBs) using the Type I Fundamental Plane, a correlation between the spectral peak energy $E_{\rm p}$, the peak luminosity $L_{\rm p}$, and the luminosity time $T_{\rm L}$ ($\equiv E_{\rm iso}/L_{\rm p}$ where $E_{\rm iso}$ is isotropic energy) for small Absolute Deviation from Constant Luminosity(ADCL). The Type I Fundamental Plane of LGRBs is calibrated using 8 LGRBs with redshift $z1.4$) to 557 SNeIa distance moduli ($z<1.4$) significantly improves the constraint for non-flat $\Lambda$CDM universe from ($\Omega_{\rm M}, \Omega_{\rm \Lambda}$)=($0.29\pm0.10$, $0.76\pm0.13$) for SNeIa only to ($\Omega_{\rm M}, \Omega_{\rm \Lambda}$)=($0.23\pm0.06$, $0.68\pm0.08$) for SNeIa and 9 LGRBs.

Cosmic acceleration with cosmological soft phonons [Replacement]

astro-ph — Thu, 17 May 2012 00:31:44 +0000

The dark energy scalar field is here presented as a mean-field effect arising from the collective motion of interacting structures on an expanding lattice. This cosmological analogue to solid-state soft phonons in an unstable crystal network is shown to produce cosmic acceleration while mimicking phantom equation of state. From an analysis of the Hubble diagram of type Ia supernovae, we present constraints on the parameters of the cosmic Lagrange chain, as well as on time-variation of the soft phonon equation of state, before we conclude on new phenomenology associated to this interpretation.

A Born-Infeld-like f(R) gravity [Replacement]

astro-ph — Thu, 17 May 2012 00:31:32 +0000

Several features of an $f(R)$ theory in which there is a maximum value for the curvature are analyzed. The theory admits the vaccuum solutions of GR, and also the radiation evolution for the scale factor of the standard cosmological model. Working in the Jordan frame, a complete analysis of the phase space is performed, and its results supported with examples obtainted by numerical integration. In particular, we showed that theory has nonsingular cosmological solutions which after the bounce enter a phase of de Sitter expansion and subsequently relax to a GR-like radiation-dominated evolution.

A Lyman Alpha Galaxy at Redshift z=6.944 in the COSMOS Field

astro-ph — Wed, 16 May 2012 01:06:19 +0000

Lyman-alpha emitting galaxies can be used to study cosmological reionization, because a neutral intergalactic medium scatters Lyman-alpha photons into diffuse halos whose surface brightness falls below typical survey detection limits. Here we present the Lyman-alpha emitting galaxy LAE J095950.99+021219.1, identified at redshift z=6.944 in the COSMOS field using narrowband imaging and followup spectroscopy with the IMACS instrument on the Magellan I Baade telescope. With a single object spectroscopically confirmed so far, our survey remains consistent with a wide range of IGM neutral fraction at redshift seven, but further observations are planned and will help clarify the situation. Meantime, the object we present here is only the third Lyman-alpha selected galaxy to be spectroscopically confirmed at redshift seven, and is 2–3 times fainter than the previously confirmed redshift seven Lyman alpha galaxies.

The optically unbiased GRB host (TOUGH) survey. I. Survey design and catalogs

astro-ph — Wed, 16 May 2012 01:06:01 +0000

Long-duration gamma-ray bursts (GRBs) are powerful tracers of star-forming galaxies at a very wide range of redshifts. We have defined a homogeneous subsample of 69 Swift GRB-selected galaxies. Special attention has been devoted to making the sample optically unbiased through simple and well-defined selection criteria based on the high-energy properties of the bursts and their positions on the sky. Thanks to our extensive follow-up observations, this sample has now achieved a comparatively high degree of redshift completeness, and thus provides a legacy sample, useful for statistical studies of GRBs and their host galaxies. In this paper we present the survey design and summarize the results of our observing program conducted at the ESO Very Large Telescope aimed at obtaining the most basic properties of galaxies in this sample, including a catalog of R and K magnitudes and redshifts. We detect the host galaxies for 80 % of the GRBs in the sample, although only 42 % Ks-band detections, which confirms that GRB-selected host galaxies are generally blue. The sample is not uniformly blue, however, with two extremely red objects detected. Moreover, galaxies hosting GRBs with no optical afterglows, whose identification therefore relies on X-ray localisations, are significantly brighter and redder than those with an optical afterglow. Our spectroscopic campaign has resulted in 77 % now having redshift measurements, with a median redshift of 2.14 +- 0.18. TOUGH alone consists of 17 detected z > 2 Swift GRB host galaxies suitable for individual and statistical studies. Seven hosts have detections of the Ly-alpha emission line and we can exclude an early indication that Ly-alpha emission is ubiquitous among GRB hosts, but confirm that Ly-alpha is stronger in GRB-selected galaxies than in flux-limited samples of Lyman break galaxies.

Hydrodynamical simulations of galaxy clusters in dark energy cosmologies: II. c-M relation

astro-ph — Wed, 16 May 2012 01:05:43 +0000

We use hydrodynamical simulations of different dark energy cosmologies to investigate the concentration-mass (c-M) relation in galaxy clusters. In particular, we consider a reference \Lambda CDM model, two quintessence models with inverse power-law potentials (RP and SUGRA), and two extended quintessence models, one with positive and one with negative coupling with gravity (EQp and EQn respectively). All the models are normalized in order to match CMB data from WMAP3. We fit both the dark matter only and the total mass profile with a NFW profile, and recover the concentration of each halo from the fit using different definition. We consider both the complete catalog of clusters and groups and subsamples of objects at different level of relaxation. We find that the definition itself of the concentration can lead to differences up to 20% in its value and that these differences are smaller when more relaxed objects are considered. The c-M relation of our reference \Lambda CDM model is in good agreement with the results in literature, and relaxed objects have a higher normalization and a shallower slope with respect to the complete sample. The inclusion of baryon physics is found to influence more high-mass systems than low-mass ones, due to a higher concentration of baryons in the inner regions of massive halos. For the different dark energy models, we find that for \Lambda CDM, RP and SUGRA the normalization of the c-M relation is linked to the growth factor, with models having a higher value of \sigma 8 D+ having also a higher normalization. This simple scheme is no longer valid for EQp and EQn because these models, depending on the sign of the coupling, have different values of the linear density contrast, leading to a decrease of the expected normalization in EQp and an increase in EQn. [Abridged]

Can we really measure fnl from the galaxy power spectrum?

astro-ph — Wed, 16 May 2012 01:05:17 +0000

The scale-dependent galaxy bias generated by primordial non-Gaussianity (PNG) can be used to detect and constrain deviations from standard single-field inflation. The strongest signal is expected in the local model for PNG, where the amplitude of non-Gaussianity can be expressed by a set of parameters (fnl, gnl, …). Current observational constraints from galaxy clustering on fnl and gnl assume that the others PNG parameters are vanishing. Using two sets of cosmological N-body simulations where both fnl and gnl are non-zero, we show that this strong assumption generally leads to biased estimates and spurious redshift dependencies of the parameters. Additionally, if the signs of fnl and gnl are opposite, the amplitude of the scale-dependent bias is reduced, possibly leading to a false null detection. Finally we show that model selection techniques like the Bayesian evidence can (and should) be used to determine if more than one PNG parameter is required by the data.

Screening Modifications of Gravity through Disformally Coupled Fields

astro-ph — Wed, 16 May 2012 01:04:48 +0000

It is shown that extensions to General Relativity, which introduce a strongly coupled scalar field, can be viable if the interaction has a non-conformal form. Such disformal coupling depends upon the gradients of the scalar field. Thus, if the field is locally static and smooth, the coupling becomes invisible in the solar system: this is the disformal screening mechanism. A cosmological model is considered where the disformal coupling triggers the onset of accelerated expansion after a scaling matter era, giving a good fit to a wide range of observational data. Moreover, the interaction leaves signatures in the formation of large-scale structure that can be used to probe such couplings.

Radio Broadcasts from Superconducting Strings

astro-ph — Wed, 16 May 2012 00:59:56 +0000

Superconducting cosmic strings can give transient electromagnetic signatures that we argue are most evident at radio frequencies. We investigate the three different kinds of radio bursts from cusps, kinks, and kink-kink collisions on superconducting strings. We find that the event rate is dominated by kink bursts in a range of parameters that are of observational interest, and can be quite high (several a day at 1 Jy flux) for a canonical set of parameters. In the absence of events, the search for radio transients can place stringent constraints on superconducting cosmic strings.

Metallicities of Emission-Line Galaxies from HST ACS PEARS and HST WFC3 ERS Grism Spectroscopy at 0.6 < z < 2.4

astro-ph — Wed, 16 May 2012 00:58:56 +0000

Galaxies selected on the basis of their emission line strength show low metallicities, regardless of their redshifts. We conclude this from a sample of faint galaxies at redshifts between 0.6 < z < 2.4, selected by their prominent emission lines in low-resolution grism spectra in the optical with the Advanced Camera for Surveys (ACS) on the Hubble Space Telescope (HST) and in the near-infrared using Wide-Field Camera 3 (WFC3). Using a sample of 11 emission line galaxies (ELGs) at 0.6 < z < 2.4 with luminosities of -22 < M_B < -19, which have [OII], H\beta, and [OIII] line flux measurements from the combination of two grism spectral surveys, we use the R23 method to derive the gas-phase oxygen abundances: 7.5 < 12+log(O/H) < 8.5. The galaxy stellar masses are derived using Bayesian based Markov Chain Monte Carlo (\piMC^2) fitting of their Spectral Energy Distribution (SED), and span the mass range 8.1 < log(M_*/M_\sun) < 10.1. These galaxies show a mass-metallicity (M-L) and Luminosity-Metallicity (L-Z) relation, which is offset by –0.6 dex in metallicity at given absolute magnitude and stellar mass relative to the local SDSS galaxies, as well as continuum selected DEEP2 samples at similar redshifts. The emission-line selected galaxies most resemble the local "green peas" galaxies and Lyman-alpha galaxies at z~0.3 and z~2.3 in the M-Z and L-Z relations and their morphologies. The G-M_{20} morphology analysis shows that 10 out of 11 show disturbed morphology, even as the star-forming regions are compact. These galaxies may be intrinsically metal poor, being at early stages of formation, or the low metallicities may be due to gas infall and accretion due to mergers.

Rapid variability of the compact radio sources in Arp220. Evidence for a population of microblazars?

astro-ph — Wed, 16 May 2012 00:57:05 +0000

Context. The two nuclei of the starburst galaxy Arp220 contain multiple compact radio sources previously identified as radio supernovae or supernova remnants. Aims. In order to search for an embedded radio AGN, or other possible exotic objects, we have carried out a program of VLBI monitoring at 6 cm over three epochs each separated by four months. Methods. Combining the new data with existing data at 6 cm and 18 cm (spanning 4 and 12 years respectively) we are able to characterise source flux density variability on a range of time-scales. Additionally we analyse the variability of sources in shape and position. Results. We detect rapid ( 4c) of jet-like features near rapidly varying almost stationary components. These enigmatic sources might be associated with an AGN or a highly beamed microquasar (i.e. microblazar). Other hypotheses include that the apparent variability is intrinsic and is produced by neutron star powered central components within a supernova remnant, by a sequence of several supernovae within super star clusters, or is extrinsic and is produced by Galactic interstellar scintillation of very compact non-varying objects. Conclusions. A microquasar/microblazar origin seems to be the best explanation for the nature of the variable sources in Arp220.

Maximally Star-Forming Galactic Disks II. Vertically-Resolved Hydrodynamic Simulations of Starburst Regulation

astro-ph — Wed, 16 May 2012 00:56:45 +0000

We explore the self-regulation of star formation using a large suite of high resolution hydrodynamic simulations, focusing on molecule-dominated regions (galactic centers and [U]LIRGS) where feedback from star formation drives highly supersonic turbulence. In equilibrium the total midplane pressure, dominated by turbulence, must balance the vertical weight of the ISM. Under self-regulation, the momentum flux injected by feedback evolves until it matches the vertical weight. We test this flux balance in simulations spanning a range of parameters, including surface density $\Sigma$, momentum injected per stellar mass formed ($p_*/m_*$), and angular velocity. The simulations are 2D radial-vertical slices, including both self-gravity and an external potential that confines gas to the disk midplane. After the simulations reach a steady state in all relevant quantities, including the star formation rate $\Sigma_{SFR}$, there is remarkably good agreement between the vertical weight, the turbulent pressure, and the momentum injection rate from supernovae. Gas velocity dispersions and disk thicknesses increase with $p_*/m_*$. The efficiency of star formation per free-fall time at the mid-plane density is insensitive to the local conditions and to the star formation prescription in very dense gas. We measure efficiencies $\sim$0.004-0.01, consistent with low and approximately constant efficiencies inferred from observations. For $\Sigma\in$(100–1000) \msunpc, we find $\Sigma_{SFR}\in$(0.1–4) \sfrunits, generally following a $\Sigma_{SFR}\propto \Sigma^2$ relationship. The measured relationships agree very well with vertical equilibrium and with turbulent energy replenishment by feedback within a vertical crossing time. These results, along with the observed $\Sigma_{SFR}-\Sigma$ relation in high density environments, provide strong evidence for the self-regulation of star formation.

Globular cluster systems as tracers of environmental effects on Virgo early-type dwarfs

astro-ph — Wed, 16 May 2012 00:55:00 +0000

Early-type dwarfs (dEs) are by far the most abundant galaxy population in nearby clusters. Whether these objects are primordial, or the recent end-products of the different physical mechanisms that can transform galaxies once they enter these high-density environments, is still a matter of debate. Here we present a novel approach to test these scenarios by comparing the properties of the globular cluster systems (GCSs) of Virgo dEs and their potential progenitors with simple predictions from gravitational and hydrodynamical interaction models. We show that low-mass (Mstar < 2E8 Msun) dEs have GCSs consistent with being the descendants of gas-stripped late-type dwarfs. On the other hand, higher mass dEs have properties -including the high mass specific frequencies of their GCSs and their concentrated spatial distribution within Virgo- incompatible with a recent, environmentally-driven evolution. They mostly comprise nucleated systems, but also dEs with recent star formation and/or disc features. Bright, nucleated dEs appear to be a population that has long resided within the cluster potential well, but have surprisingly managed to retain very rich and spatially extended GCSs – possibly an indication of high total masses. Our analysis does not favour violent evolutionary mechanisms that result in significant stellar mass losses, but more gentle processes involving gas removal by a combination of internal and external factors, and highlights the relevant role of initial conditions. Additionally, we briefly comment on the origin of luminous cluster S0s.

Second-order matter fluctuations via higher-order galaxy correlators

astro-ph — Wed, 16 May 2012 00:51:57 +0000

We provide a formula for extracting the value of the rms of the linear matter fluctuations on a scale R directly from redshift surveys data. It allows to constrain the real-space amplitude of sigma_R without requiring any modeling of the nature and power spectrum of the matter distribution. Furthermore, the formalism is completely insensitive to the character of the bias function, namely its eventual scale or non-linear dependence. By contrasting measurements of sigma_R with predictions from linear perturbation theory, one can test for eventual departures from the standard description of gravity on large cosmological scales. The proposed estimator exploits the information contained in the 1-point moments and 2-point correlators of the matter and galaxy density fields, and it can be applied on cosmic scales where linear and semi-linear perturbative approximations of the evolution of matter overdensities offer a satisfactory description of the full underlying theory. We implement the test with N-body simulations to quantify potential systematics and successfully show that we are able to recover the present day value of sigma_8 `hidden’ in the simulation. We also design a consistency check to gauge the soundness of the results inferred when the formalism is applied to real (as opposed to simulated) data. We expect that this approach will provide a sensitive probe of the clustering of matter when applied to future large redshift survey such as BigBOSS and EUCLID.

Simultaneous Ultraviolet and Optical Emission-line Profiles of Quasars: Implications for Black Hole Mass Determination

astro-ph — Wed, 16 May 2012 00:50:39 +0000

The X-shooter instrument on the VLT was used to obtain spectra of seven moderate-redshift quasars simultaneously covering the spectral range 3000 Ang to 2.5 microns. At z ~ 1.5, most of the prominent broad emission lines in the ultraviolet to optical region are captured in their rest frame. We use this unique dataset, which mitigates complications from source variability, to intercompare the line profiles of C IV 1549, C III] 1909, Mg II 2800, and Halpha and evaluate their implications for black hole mass estimation. We confirm that Mg II and the Balmer lines share similar kinematics and that they deliver mutually consistent black hole mass estimates with minimal internal scatter (< 0.1 dex) using the latest virial mass estimators. Although no virial mass formalism has yet been calibrated for C III], this line does not appear promising for such an application because of the large spread of its velocity width compared to lines of both higher and lower ionization; part of the discrepancy may be due to the difficulty of deblending C III] from its neighboring lines. The situation for C IV is complex and, because of the limited statistics of our small sample, inconclusive. On the one hand, slightly more than half of our sample (4/7) have C IV line widths that correlate reasonably well with Halpha line widths, and their respective black hole mass estimates agree to within ~0.15 dex. The rest, on the other hand, exhibit exceptionally broad C IV profiles that overestimate virial masses by factors of 2-5 compared to Halpha. As C IV is widely used to study black hole demographics at high redshifts, we urgently need to revisit our analysis with a larger sample.

Incidence of Mg II absorption systems towards flat-spectrum radio quasars

astro-ph — Wed, 16 May 2012 00:47:29 +0000

The conventional wisdom that the rate of incidence of Mg II absorption systems, dN/dz (excluding `associated systems’ having velocity beta*c relative to the AGN of less than ~5000 km/s) is totally independent of the background AGN, has been challenged by a recent finding that dN/dz for strong Mg II absorption systems towards distant blazars is 2.2 \pm_{0.6}^{0.8} times the value known for normal optically-selected quasars (QSOs). This has led to the suggestion that a significant fraction of even the absorption systems with beta as high as 0.1 may have been ejected by the relativistic jets in the blazars, which are expected to be pointed close to our direction. Here we investigate this scenario using a large sample of 115 flat-spectrum radio-loud quasars (FSRQs) which too possess powerful jets, but are only weakly polarized. We show, for the first time, that dN/dz towards FSRQs is, on the whole, quite similar to that known for QSOs and the comparative excess of strong \mgii absorption systems seen towards blazars is mainly confined to beta< 0.15. The excess relative to FSRQs can probably result from a likely closer alignment of blazar jets with our direction and hence any gas clouds accelerated by them are more likely to be on the line of sight to the active quasar nucleus.

Generalized dark gravity [Cross-Listing]

astro-ph — Wed, 16 May 2012 00:46:38 +0000

The late-time cosmic acceleration may be due to infra-red modifications of General Relativity. In particular, we consider a maximal extension of the Hilbert-Einstein action and analyze several interesting features of the theory. Generally, the motion is non-geodesic and takes place in the presence of an extra force, which is orthogonal to the four-velocity. These models could lead to some major differences, as compared to the predictions of General Relativity or other modified theories of gravity, in several problems of current interest, such as cosmology, gravitational collapse or the generation of gravitational waves. The study of these phenomena may also provide some specific signatures and effects, which could distinguish and discriminate between the various gravitational models.

Issues about vacuum energy as the origin of dark energy [Cross-Listing]

astro-ph — Wed, 16 May 2012 00:46:02 +0000

In this letter we address some of the issues raised in the literature about the conflict between a large vacuum energy density, a priori predicted by quantum field theory, and the observed dark energy which must be the energy of vacuum or include it. We present a number of arguments against this claim and in favour of a null vacuum energy. They are based on: a new definition for the vacuum in quantum field theory as a frame-independent coherent state, results from a detailed study of condensation of scalar fields in FLRW background performed in a previous work, and our present knowledge about the Standard Model of particle physics. One of the predictions of these arguments is the confinement of nonzero expectation value of Higgs field to scales roughly comparable with the width of electroweak gauge bosons or shorter. If the observation of Higgs by the LHC is confirmed, accumulation of relevant events and their energy dependence in near future should allow to test the spatial extend of the Higgs condensate.

The Scale of Cosmic Isotropy

astro-ph — Wed, 16 May 2012 00:45:42 +0000

The most fundamental premise to the standard model of the universe, the Cosmological Principle (CP), states that the large-scale properties of the universe are the same in all directions and at all comoving positions. Demonstrating this theoretical hypothesis has proven to be a formidable challenge. The cross-over scale R_{iso} above which the galaxy distribution becomes statistically isotropic is vaguely defined and poorly (if not at all) quantified. Here we report on a formalism that allows us to provide an unambiguous operational definition and an estimate of R_{iso}. We apply the method to galaxies in the Sloan Digital Sky Survey (SDSS) Data Release 7, finding that R_{iso}\sim 150h^{-1} Mpc. Besides providing a consistency test of the Copernican principle, this result is in agreement with predictions based on numerical simulations of the spatial distribution of galaxies in cold dark matter dominated cosmological models.

A mid-IR survey of local AGN with GTC/CanariCam

astro-ph — Wed, 16 May 2012 00:45:02 +0000

We describe a mid-infrared (MIR) survey of local AGN to be conducted with the CanariCam instrument on the Gran Telescopio Canarias (GTC). We will obtain MIR imaging and spectroscopy of a sample of ~100 AGN covering six orders of magnitude in AGN luminosity, and including different AGN classes (e.g., LINERs, Seyfert 1s and 2s, QSO). The main goals are: (1) to test unification of Type 1 and Type 2 AGN, (2) to study the star formation activity around AGN, and (3) to explore the role of the dusty torus in low-luminosity AGN.

Cosmic acceleration with cosmological soft phonons

astro-ph — Wed, 16 May 2012 00:44:31 +0000

Everything You Always Wanted To Know About The Cosmological Constant Problem (But Were Afraid To Ask)

astro-ph — Wed, 16 May 2012 00:43:58 +0000

This article aims at discussing the cosmological constant problem at a pedagogical but fully technical level. We review how the vacuum energy can be regularized in flat and curved space-time and how it can be understood in terms of Feynman bubble diagrams. In particular, we show that the properly renormalized value of the zero-point energy density today (for a free theory) is in fact far from being 122 orders of magnitude larger than the critical energy density, as often quoted in the literature. We mainly consider the case of scalar fields but also treat the cases of fermions and gauge bosons which allows us to discuss the question of vacuum energy in super-symmetry. Then, we discuss how the cosmological constant can be measured in cosmology and constrained with experiments such as measurements of planet orbits in our solar system or atomic spectra. We also review why the Lamb shift and the Casimir effect seem to indicate that the quantum zero-point fluctuations are not an artifact of the quantum field theory formalism. We investigate how experiments on the universality of free fall can constrain the gravitational properties of vacuum energy and we discuss the status of the weak equivalence principle in quantum mechanics, in particular the Collela, Overhausser and Werner experiment and the quantum Galileo experiment performed with a Salecker-Wigner-Peres clock. Finally, we briefly conclude with a discussion on the solutions to the cosmological constant problem that have been proposed so far.

Vector and Tensor Contributions to the Luminosity Distance

astro-ph — Wed, 16 May 2012 00:43:45 +0000

We compute the vector and tensor contributions to the luminosity distance fluctuations in first order perturbation theory and we expand them in spherical harmonics. This work presents the formalism with a first application to a stochastic background of primordial gravitational waves.

Galaxy And Mass Assembly (GAMA): Galaxy environments and star formation rate variations

astro-ph — Wed, 16 May 2012 00:43:18 +0000

We present a detailed investigation into the effects of galaxy environment on their star formation rates (SFR) using galaxies observed in the Galaxy and Mass Assembly Survey (GAMA). We use three independent volume-limited samples of galaxies within z < 0.2 and Mr < -17.8. We investigate the known SFR-density relationship and explore in detail the dependence of SFR on stellar mass and density. We show that the SFR-density trend is only visible when we include the passive galaxy population along with the star-forming population. This SFR-density relation is absent when we consider only the star-forming population of galaxies, consistent with previous work. While there is a strong dependence of the EWH?a on density we find, as in previous studies, that these trends are largely due to the passive galaxy population and this relationship is absent when considering a "star-forming" sample of galaxies. We find that stellar mass has the strongest influence on SFR and EWH?a with the environment having no significant effect on the star-formation properties of the star forming population. We also show that the SFR-density relationship is absent for both early and late-type star-forming galaxies. We conclude that the stellar mass has the largest impact on the current SFR of a galaxy, and any environmental effect is not detectable. The observation that the trends with density are due to the changing morphology fraction with density implies that the timescales must be very short for any quenching of the SFR in infalling galaxies. Alternatively galaxies may in fact undergo predominantly in-situ evolution where the infall and quenching of galaxies from the field into dense environments is not the dominant evolutionary mode.

Planck Intermediate Results. IV. The XMM-Newton validation programme for new Planck clusters

astro-ph — Wed, 16 May 2012 00:42:36 +0000

Scale dependent halo bias in the excursion set approach

astro-ph — Wed, 16 May 2012 00:41:56 +0000

If one accounts for correlations between scales, then nonlocal, k-dependent halo bias is part and parcel of the excursion set approach, and hence of halo model predictions for galaxy bias. We present an analysis that distinguishes between a number of different effects, each one of which contributes to scale-dependent bias in real space. We show how to isolate these effects and remove the scale dependence, order by order, by cross-correlating the halo field with suitably transformed versions of the mass field. These transformations may be thought as simple one-point, two-scale measurements that allow one to estimate quantities which are usually constrained using n-point statistics. As part of our analysis, we present a simple analytic approximation for the first crossing distribution of walks with correlated steps which are constrained to pass through a specified point, and demonstrate its accuracy. Although we concentrate on nonlinear, nonlocal bias with respect to a Gaussian random field, we show how to generalize our analysis to more general fields.

Hawking Radiation as a Mechanism for Inflation [Cross-Listing]

astro-ph — Wed, 16 May 2012 00:40:51 +0000

The Friedman-Robertson-Walker (FRW) space-time exhibits particle creation similar to Hawking radiation of a black hole. In this essay we show that this FRW Hawking radiation leads to an effective negative pressure fluid which can drive an inflationary period of exponential expansion in the early Universe. Since the Hawking temperature of the FRW space-time decreases as the Universe expands this mechanism naturally turns off and the inflationary stage transitions to a power law expansion associated with an ordinary radiation dominated Universe.

Dark energy cosmology: the equivalent description via different theoretical models and cosmography tests [Cross-Listing]

astro-ph — Wed, 16 May 2012 00:40:32 +0000

We review different dark energy cosmologies. In particular, we present the $\Lambda$CDM cosmology, Little Rip and Pseudo-Rip universes, the phantom and quintessence cosmologies with Type I, II, III and IV finite-time future singularities and non-singular dark energy universes. In the first part, we explain the $\Lambda$CDM model and well-established observational tests which constrain the current cosmic acceleration. After that, we investigate the dark fluid universe where a fluid has quite general equation of state (EoS) [including inhomogeneous or imperfect EoS]. All the above dark energy cosmologies for different fluids are explicitly realized, and their properties are also explored. It is shown that all the above dark energy universes may mimic the $\Lambda$CDM model currently, consistent with the recent observational data. Furthermore, special attention is paid to the equivalence of different dark energy models. We consider single and multiple scalar field theories, tachyon scalar theory and holographic dark energy as models for current acceleration with the features of quintessence/phantom cosmology, and demonstrate their equivalence to the corresponding fluid descriptions. In the second part, we study another equivalent class of dark energy models which includes $F(R)$ gravity as well as $F(R)$ Ho\v{r}ava-Lifshitz gravity and the teleparallel $f(T)$ gravity. The cosmology of such models representing the $\Lambda$CDM-like universe or the accelerating expansion with the quintessence/phantom nature is described. Finally, we approach the problem of testing dark energy and alternative gravity models to general relativity by cosmography. We show that degeneration among parameters can be removed by accurate data analysis of large data samples and also present the examples.

Comparing galaxy populations in compact and loose groups of galaxies

astro-ph — Wed, 16 May 2012 00:40:13 +0000

We perform a comparison of the properties of galaxies in compact groups, loose groups and in the field to deepen our understanding of the physical mechanisms acting upon galaxy evolution in different environments. We select samples of galaxies in compact groups identified by McConnachie et al., loose groups identified by Zandivarez and Martinez, and field galaxies from the Sloan Digital Sky Survey. We compare properties of the galaxy populations in these different environments: absolute magnitude, colour, size, surface brightness, stellar mass and concentration. We also study the fraction of red and early type galaxies, the luminosity function, the colour-luminosity and luminosity-size relations. The population of galaxies in compact groups differ from that of loose groups and the field. The fraction of read and early type galaxies is higher in compact groups. On average, galaxies in compact groups are systematically smaller, more concentrated and have higher surface brightness than galaxies in the field and in loose groups. For fixed absolute magnitude, or fixed surface brightness, galaxies in compact groups are smaller. The physical mechanisms that transform galaxies into earlier types could be more effective within compact groups given the high densities and low velocity dispersion that characterise that particular environment, this could explain the large fraction of red and early type galaxies we found in compact groups. Galaxies inhabiting compact groups have undergone a major transformation compared to galaxies that inhabit loose groups.

Using H(z) data as a probe of the concordance model

astro-ph — Wed, 16 May 2012 00:39:57 +0000

Direct observations of the Hubble rate, from cosmic chronometers and the radial baryon acoustic oscillation scale, can out-perform supernovae observations in understanding the expansion history, because supernovae observations need to be differentiated to extract H(z). We use existing H(z) data and smooth the data using a new Gaussian Processes package, GaPP, from which we can also estimate derivatives. The obtained Hubble rate and its derivatives are used to reconstruct the equation of state of dark energy and to perform consistency tests of the LCDM model, some of which are newly devised here. Current data is consistent with the concordance model, but is rather sparse. Future observations will provide a dramatic improvement in our ability to constrain or refute the concordance model of cosmology. We produce simulated data to illustrate how effective H(z) data will be in combination with Gaussian Processes.

Imaging neutral hydrogen on large-scales during the Epoch of Reionization with LOFAR

astro-ph — Wed, 16 May 2012 00:39:23 +0000

The first generation of redshifted 21 cm detection experiments, carried out with arrays like LOFAR, MWA and GMRT, will have a very low signal-to-noise ratio per resolution element (\sim 0.2). In addition, whereas the variance of the cosmological signal decreases on scales larger than the typical size of ionization bubbles, the variance of the formidable galactic foregrounds increases, making it hard to disentangle the two on such large scales. The poor sensitivity on small scales on the one hand, and the foregrounds effect on large scales on the other hand, make direct imaging of the Epoch of Reionization of the Universe very difficult, and detection of the signal therefore is expected to be statistical.Despite these hurdles, in this paper we argue that for many reionization scenarios low resolution images could be obtained from the expected data. This is because at the later stages of the process one still finds very large pockets of neutral regions in the IGM, reflecting the clustering of the large-scale structure, which stays strong up to scales of \sim 120 comoving Mpc/h (\sim 1 degree). The coherence of the emission on those scales allows us to reach sufficient S/N (\sim 3) so as to obtain reionization 21 cm images. Such images will be extremely valuable for answering many cosmological questions but above all they will be a very powerful tool to test our control of the systematics in the data. The existence of this typical scale (\sim 120 comoving Mpc/h) also argues for designing future EoR experiments, e.g., with SKA, with a field of view of at least 4 degree.

A Born-Infeld-like f(R) gravity [Cross-Listing]

astro-ph — Wed, 16 May 2012 00:37:58 +0000

Quasar feedback in the early Universe: the case of SDSS J1148+5251

astro-ph — Wed, 16 May 2012 00:36:57 +0000

Galaxy-scale gas outflows triggered by active galactic nuclei have been proposed as a key physical process to regulate the co-evolution of nuclear black holes and their host galaxies. The recent detection of a massive gas outflow in one of the most distant quasar, SDSS J1148+5251 at z = 6.4, presented by Maiolino et al. (2012) strongly supports this idea and suggests that strong quasar feedback is already at work at very early times. In a previous work, Valiante et al. (2011), we have presented a hierarchical semi-analytical model, GAMETE/ QSOdust, for the formation and evolution of high-redshift quasars, and we have applied it to the quasar SDSS J1148+5251, with the aim of investigating the star formation history, the nature of the dominant stellar populations and the origin and properties of the large dust mass observed in the host galaxy. A robust prediction of the model is that the evolution of the nuclear black hole and of the host galaxy are tightly coupled by quasar feedback in the form of strong galaxy-scale winds. In the present letter, we show that the gas outflow rate predicted by GAMETE/QSOdust is in good agreement with the lower limit of 3500 Msun/yr inferred by the observations. According to the model, the observed outflow at z = 6.4 is dominated by quasar feedback, as the outflow rate has already considerably depleted the gas content of the host galaxy, leading to a down-turn in the star formation rate at z < 7 – 8. Hence, supernova explosions give a negligible contribution to the observed winds at z = 6.4, driving outflow with a rate of < 10 Msun/yr.

Radiation Pressure Driven Galactic Winds from Self-Gravitating Discs [Replacement]

astro-ph — Wed, 16 May 2012 00:36:48 +0000

(Abridged) We study large-scale winds driven from uniformly bright self-gravitating discs radiating near the Eddington limit. We show that the ratio of the radiation pressure force to the gravitational force increases with height above the disc surface to a maximum of twice the value of the ratio at the disc surface. Thus, uniformly bright self-gravitating discs radiating at the Eddington limit are fundamentally unstable to driving large-scale winds. These results contrast with the spherically symmetric case, where super-Eddington luminosities are required for wind formation. We apply this theory to galactic winds from rapidly star-forming galaxies that approach the Eddington limit for dust. For hydrodynamically coupled gas and dust, we find that the asymptotic velocity of the wind is v_\infty ~ 1.5 v_rot and that v_\infty SFR^{0.36}, where v_rot is the disc rotation velocity and SFR is the star formation rate, both of which are in agreement with observations. However, these results of the model neglect the gravitational potential of the surrounding dark matter halo and an old passive stellar bulge or extended disc, which act to decrease v_\infty. A more realistic treatment shows that the flow can either be unbound, or bound, forming a “fountain flow” with a typical turning timescale of t_turn ~ 0.1-1 Gyr. We provide quantitative criteria and scaling relations for assessing whether or not a rapidly star-forming galaxy of given properties can drive unbound flows via the mechanism described in this paper. Importantly, we note that because t_turn is longer than the star formation timescale in the rapidly star-forming galaxies and ULIRGs for which our theory is most applicable, if rapidly star-forming galaxies are selected as such, they may be observed to have strong outflows, even though their winds are eventually bound on large scales.

Space-time variation of the electron-to-proton mass ratio in a Weyl model [Replacement]

astro-ph — Wed, 16 May 2012 00:36:28 +0000

Seeking a possible explanation for recent data indicating a space-time variation of the electron-to-proton mass ratio within the Milky Way, we consider a phenomenological model where the effective fermion masses depend on the local value of the Weyl tensor. We contrast the required values of the model’s free parameters with bounds obtained from modern tests on the violation of the Weak Equivalence Principle and we find that these quantities are incompatible. This result indicates that the variation of nucleon and electron masses through a coupling with the Weyl tensor is not a viable model.

Flavored Co-annihilations [Replacement]

astro-ph — Wed, 16 May 2012 00:36:18 +0000

Neutralino dark matter in supersymmetric models is revisited in the presence of flavor violation in the soft supersymmetry breaking sector. We focus on flavor violation in the sleptonic sector and study the implications for the co-annihilation regions. Flavor violation is introduced by a single $\tilde{\mu}_R-\tilde{\tau}_R$ insertion in the slepton mass matrix. Limits on this insertion from BR($\tau \to \mu + \gamma$) are weak in some regions of the parameter space where cancellations happen within the amplitudes. We look for overlaps in parameter space where both the co-annihilation condition as well as the cancellations within the amplitudes occur. In mSUGRA, such overlap regions are not existent, whereas they are present in models with non-universal Higgs boundary conditions (NUHM). The effect of flavor violation is two fold: (a) it shifts the co-annihilation regions towards lighter neutralino masses (b) the co-annihilation cross sections would be modified with the inclusion of flavor violating diagrams which can contribute significantly. Even if flavor violation is within the presently allowed limits, this is sufficient to modify the thermally averaged cross-sections by about (10-15)% in mSUGRA and (20-30)% in NUHM, depending on the parameter space. In the overlap regions, the flavor violating cross sections become comparable and in some cases even dominant to the flavor conserving ones. A comparative study of the channels is presented for mSUGRA and NUHM cases.

A kinetic theory of diffusion in general relativity with cosmological scalar field [Replacement]

astro-ph — Wed, 16 May 2012 00:35:55 +0000

A new model to describe the dynamics of particles undergoing diffusion in general relativity is proposed. The evolution of the particle system is described by a Fokker-Planck equation without friction on the tangent bundle of spacetime. It is shown that the energy-momentum tensor for this matter model is not divergence-free, which makes it inconsistent to couple the Fokker-Planck equation to the Einstein equations. This problem can be solved by postulating the existence of additional matter fields in spacetime or by modifying the Einstein equations. The case of a cosmological scalar field term added to the left hand side of the Einstein equations is studied in some details. For the simplest cosmological model, namely the flat Robertson-Walker spacetime, it is shown that, depending on the initial value of the cosmological scalar field, which can be identified with the present observed value of the cosmological constant, either unlimited expansion or the formation of a singularity in finite time will occur in the future. Future collapse into a singularity also takes place for a suitable small but positive present value of the cosmological constant, in contrast to the standard diffusion-free scenario.

Cosmic Rays during BBN as Origin of Lithium Problem [Replacement]

astro-ph — Wed, 16 May 2012 00:35:21 +0000

There may be non-thermal cosmic rays during big-bang nucleosynthesis (BBN) epoch (dubbed as BBNCRs). This paper investigated whether such BBNCRs can be the origin of Lithium problem or not. It can be expected that BBNCRs flux will be small in order to keep the success of standard BBN (SBBN). With favorable assumptions on the BBNCR spectrum between 0.09 — 4 MeV, our numerical calculation showed that extra contributions from BBNCRs can account for the $^7$Li abundance successfully. However $^6$Li abundance is only lifted an order of magnitude, which is still much lower than the observed value. As the deuteron abundance is very sensitive to the spectrum choice of BBNCRs, the allowed parameter space for the spectrum is strictly constrained. We should emphasize that the acceleration mechanism for BBNCRs in the early universe is still an open question. For example, strong turbulent magnetic field is probably the solution to the problem. Whether such a mechanism can provide the required spectrum deserves further studies.

Warm baryogenesis [Replacement]

astro-ph — Wed, 16 May 2012 00:35:13 +0000

We show that a baryon asymmetry can be generated by dissipative effects during warm inflation via a supersymmetric two-stage mechanism, where the inflaton is coupled to heavy mediator fields that then decay into light species through B- and CP-violating interactions. In contrast with thermal GUT baryogenesis models, the temperature during inflation is always below the heavy mass threshold, simultaneously suppressing thermal and quantum corrections to the inflaton potential and the production of dangerous GUT relics. This naturally gives a small baryon asymmetry close to the observed value, although parametrically larger values may be diluted after inflation along with any gravitino overabundance. Furthermore, this process yields baryon isocurvature perturbations within the range of future experiments, making this an attractive and testable model of GUT baryogenesis.

Static brane–like vacuum solutions in D \ge 5 dimensional spacetime with positive ADM mass but no horizon [Replacement]

astro-ph — Wed, 16 May 2012 00:35:02 +0000

We describe static, brane–like, solutions to vacuum Einstein’s equations in D = n + m + 2 dimensional spacetime with m \ge 2 and n \ge 1. These solutions have positive ADM mass but no horizon. The curvature invariants are finite everywhere except at r = 0 where r is the radial coordinate in the m + 1 dimensional space. The presence of n \ge 1 extra dimensions is crucial for these properties. Such solutions may be naturally anticipated if Mathur’s fuzzball proposal for black holes is correct.

Affleck-Dine dynamics and the dark sector of pangenesis [Replacement]

astro-ph — Wed, 16 May 2012 00:34:40 +0000

Pangenesis is the mechanism for jointly producing the visible and dark matter asymmetries via Affleck-Dine dynamics in a baryon-symmetric universe. The baryon-symmetric feature means that the dark asymmetry cancels the visible baryon asymmetry and thus enforces a tight relationship between the visible and dark matter number densities. The purpose of this paper is to analyse the general dynamics of this scenario in more detail and to construct specific models. After reviewing the simple symmetry structure that underpins all baryon-symmetric models, we turn to a detailed analysis of the required Affleck-Dine dynamics. Both gravity-mediated and gauge-mediated supersymmetry breaking are considered, with the messenger scale left arbitrary in the latter, and the viable regions of parameter space are determined. In the gauge-mediated case where gravitinos are light and stable, the regime where they constitute a small fraction of the dark matter density is identified. We discuss the formation of Q-balls, and delineate various regimes in the parameter space of the Affleck-Dine potential with respect to their stability or lifetime and their decay modes. We outline the regions in which Q-ball formation and decay is consistent with successful pangenesis. Examples of viable dark sectors are presented, and constraints are derived from big bang nucleosynthesis, large scale structure formation and the Bullet cluster. Collider signatures and implications for direct dark matter detection experiments are briefly discussed. The following would constitute evidence for pangenesis: supersymmetry, GeV-scale dark matter mass(es) and a Z’ boson with a significant invisible width into the dark sector.

Constraining the nature of the most distant Gamma-Ray Burst host galaxies [Replacement]

astro-ph — Wed, 16 May 2012 00:34:19 +0000

Long duration gamma-ray bursts (GRBs) allow us to explore the distant Universe, and are potentially the most effective tracer of the most distant objects. Our current knowledge of the properties of GRB host galaxies at redshifts >5 is very scarce. We propose to improve this situation by obtaining more observations of high-redshift hosts to better understand their properties and help enable us to use GRBs as probes of the high-redshift universe. We performed very deep photometric observations of three high-redshift GRB host galaxies, GRB 080913 at z =6.7, GRB 060927 at z =5.5 and GRB 060522 at z =5.1. In addition, we completed deep spectroscopic observations of the GRB080913 host galaxy with X-Shooter at the VLT to search for Ly-alpha emission. For the sake of the discussion, we use published results on another high-redshift GRB host, GRB 050904 at z = 6.3. The sample of GRB host galaxies studied in this paper consists of four out of the five spectroscopically confirmed GRBs at z>5. Despite our presented observations being the deepest ever reported of high-redshift GRB host galaxies, we do not detect any of the hosts, neither in photometry nor in spectroscopy in the case of GRB 080913. These observations indicate that the GRB host galaxies seem to evolve with time and to have lower SFRs at z >5 than they have at z5, our observations are not sufficiently sensitive to allow us to infer further conclusions on whether this specific population is representative of the general one. The characterization of high-redshift GRB host galaxies is a very challenging endeavor requiring a lot of telescope time, but is necessary to improve our understanding of the high-redshift universe.

CMB Lensing and Giant Rings [Replacement]

astro-ph — Wed, 16 May 2012 00:33:50 +0000

We study the CMB lensing signature of a pre-inationary particle (PIP), assuming it is responsible for the giant rings anomaly that was found recently in the WMAP data. Simulating Planck-like data we find that generically the CMB lensing signal to noise ratio associated with such a PIP is quite small and it would be difficult to cross correlate the temperature giant rings with the CMB lensing signal. However, if the pre-inationary particle is also responsible for the bulk flow measured from the local large scale structure, which happens to point roughly at the same direction as the giant rings, then the CMB lensing signal to noise ratio is fairly significant.

Earthly probes of the smallest dark matter halos [Replacement]

astro-ph — Wed, 16 May 2012 00:33:27 +0000

Dark matter kinetic decoupling involves elastic scattering of dark matter off of leptons and quarks in the early universe, the same process relevant for direct detection and for the capture rate of dark matter in celestial bodies; the resulting size of the smallest dark matter collapsed structures should thus correlate with quantities connected with direct detection rates and with the flux of high-energy neutrinos from dark matter annihilation in the Sun or in the Earth. In this paper we address this general question in the context of two widely studied and paradigmatic weakly-interacting particle dark matter models: the lightest neutralino of the minimal supersymmetric extension of the Standard Model, and the lightest Kaluza-Klein particle of Universal Extra Dimensions (UED). We argue and show that while the scalar neutralino-nucleon cross section correlates poorly with the kinetic decoupling temperature, the spin-dependent cross section exhibits a strong correlation in a wide range of models. In UED models the correlation is present for both cross sections, and is extraordinarily tight for the spin-dependent case. A strong correlation is also found, for both models, for the flux of neutrinos from the Sun, especially for fluxes large enough to be at potentially detectable levels. We provide analytic guidance and formulae that illustrate our findings.

The Advanced Camera for Surveys General Catalog: Structural Parameters for Approximately Half a Million Galaxies [Replacement]

astro-ph — Wed, 16 May 2012 00:33:06 +0000

We present the Advanced Camera for Surveys General Catalog (ACS-GC), a photometric and morphological database using publicly available data obtained with the Advanced Camera for Surveys (ACS) instrument on the Hubble Space Telescope. The goal of the ACS-GC database is to provide a large statistical sample of galaxies with reliable structural and distance measurements to probe the evolution of galaxies over a wide range of look-back times. The ACS-GC includes approximately 470,000 astronomical sources (stars + galaxies) derived from the AEGIS, COSMOS, GEMS, and GOODS surveys. Galapagos was used to construct photometric (SExtractor) and morphological (Galfit) catalogs. The analysis assumes a single S\’ersic model for each object to derive quantitative structural parameters. We include publicly available redshifts from the DEEP2, COMBO-17, TKRS, PEARS, ACES, CFHTLS,and zCOSMOS surveys to supply redshifts (spectroscopic and photometric) for a considerable fraction (~74%) of the imaging sample. The ACS-GC includes color postage stamps, Galfit residual images, and photometry, structural parameters, and redshifts combined into a single catalog.

Phantom Inflation in Little Rip [Replacement]

astro-ph — Wed, 16 May 2012 00:32:58 +0000

We study the phantom inflation in little rip cosmology, in which the current acceleration is driven by the field with the parameter of state w < -1, but since w tends to -1 asymptotically, the rip singularity occurs only at infinite time. In this scenario, before the rip singularity is arrived, the universe is in an inflationary regime. We numerically calculate the spectrum of primordial perturbation generated during this period and find that the results may be consistent with observations. This implies that if the reheating happens again, the current acceleration might be just a start of phantom inflation responsible for the upcoming observational universe.

130 GeV dark matter and the Fermi gamma-ray line [Replacement]

astro-ph — Wed, 16 May 2012 00:32:25 +0000

Based on tentative evidence for a peak in the Fermi gamma-ray spectrum originating from near the center of the galaxy, it has been suggested that dark matter of mass ~130 GeV is annihilating directly into photons with a cross section ~24 times smaller than that needed for the thermal relic density. We propose a simple particle physics model in which the DM is a scalar X, with a coupling lambda_X X^2|S|^2 to a scalar multiplet S carrying electric charge, which allows for XX -> gamma gamma at one loop due to the virtual S. We predict a second monochromatic photon peak at 114 GeV due to XX -> gamma Z. The S should be colored under a hidden sector SU(N) or QCD to confine the charged relic S. The analogous coupling lambda_h h^2 |S|^2 to the Higgs boson can naturally increase the partial width for h -> gamma gamma by an amount comparable to its standard model value, as suggested by recent measurements from CMS. Due to the hidden sector SU(N) (or QCD), S binds to its antiparticle to form S-pions, which will be pair-produced in colliders and then decay predominantly to XX, hh (or hadronic jets) and subdominantly to gamma gamma. The cross section for X on nucleons is in marginal conflict with the Xenon100 upper limit, suggesting that it should be discovered soon by direct detection.

Stripped gas as fuel for newly formed HII regions in the encounter between VCC1249 and M49: a unified picture from NGVS and GUViCS [Replacement]

astro-ph — Wed, 16 May 2012 00:31:06 +0000

Context: We study the peculiar interacting galaxy system of VCC1249/M49 located in the core of the Virgo B subcluster. Owing to a recent interaction between the dwarf galaxy VCC1249 and the halo gas of the gE M49, neutral hydrogen has been displaced from the interstellar medium of this dwarf into the Virgo ICM. Observations also reveal multiple compact star-forming regions that are embedded in this HI cloud, with a projected separation up to 13 kpc from VCC1249 in the northwest direction. Aims: Motivated by recent NUV imaging from GUViCS of the VCC1249/M49 system that shows significant ongoing/recent star formation in the compact regions, we aim to constrain the origin of these outlying HII regions with a multi-wavelength approach. Methods: Using deep optical (u, g, i, z) imaging from NGVS and new Halpha imaging obtained at the San Pedro Martir observatory together with Keck long-slit spectroscopy, we characterize the SFR, ages, and metallicity of VCC1249 and its outlying compact regions. Moreover, we analyze the color and luminosity profile of the galaxy to investigate its recent interaction with M49. Results: Our new observations indicate that VCC1249 underwent a recent interaction with M49 in which both ram-pressure stripping and tidal interaction occured. The joint action of the two mechanisms led to the removal of the HI gas from the ISM of VCC1249, while the gravitational tides triggered the stellar tail and counter-tail of VCC1249. Our SED analysis reveals that the star formation in this galaxy was truncated around 200 Myr ago and that the outlying HII regions were born in situ about 10 Myr ago out of pre-enriched gas removed from the dwarf galaxy. These observations also reveal that interactions between central and satellite galaxies similar to the one between VCC1249/M49 may be an effective way of dispersing metals into the halos of massive galaxies.

The velocity dispersion and mass function of the outer halo globular cluster Palomar 4

astro-ph — Tue, 15 May 2012 00:55:08 +0000

We obtained precise line-of-sight radial velocities of 23 member stars of the remote halo globular cluster Palomar 4 (Pal 4) using the High Resolution Echelle Spectrograph (HIRES) at the Keck I telescope. We also measured the mass function of the cluster down to a limiting magnitude of V~28 mag using archival HST/WFPC2 imaging. We derived the cluster’s surface brightness profile based on the WFPC2 data and on broad-band imaging with the Low-Resolution Imaging Spectrometer (LRIS) at the Keck II telescope. We find a mean cluster velocity of 72.55+/-0.22 km/s and a velocity dispersion of 0.87+/-0.18 km/s. The global mass function of the cluster, in the mass range 0.55<=M<=0.85 M_solar, is shallower than a Kroupa mass function and the cluster is significantly depleted in low-mass stars in its center compared to its outskirts. Since the relaxation time of Pal 4 is of the order of a Hubble time, this points to primordial mass segregation in this cluster. Extrapolating the measured mass function towards lower-mass stars and including the contribution of compact remnants, we derive a total cluster mass of 29800 M_solar. For this mass, the measured velocity dispersion is consistent with the expectations of Newtonian dynamics and below the prediction of Modified Newtonian Dynamics (MOND). Pal 4 adds to the growing body of evidence that the dynamics of star clusters in the outer Galactic halo can hardly be explained by MOND.

Shaping the galaxy stellar mass function with supernova- and AGN-driven winds

astro-ph — Tue, 15 May 2012 00:54:51 +0000

Cosmological hydrodynamical simulations of galaxy formation in representative regions of the Universe typically need to resort to subresolution models to follow some of the feedback processes crucial for galaxy formation. Here, we show that an energy-driven outflow model in which the wind velocity decreases and the wind mass loading increases in low-mass galaxies, as suggested by observations, can produce a good match to the low-mass end of the observed galaxy stellar mass function. The high-mass end can be recovered simultaneously if feedback from active galactic nuclei (AGN) and a correction for diffuse stellar light plausibly missed in observations are included. At the same time, our model is in good agreement with the stellar mass functions at redshifts z=1 and z=2, and with the observed redshift evolution of the cosmic star formation rate density. In addition, it accurately reproduces the observed gas to stellar mass ratios and specific star formation rates of galaxies as a function of their stellar mass. This agreement with a diverse set of data marks significant progress in hydrodynamically modelling the formation of a representative galaxy population. It also suggests that the mass flux in real galactic winds should strongly increase towards low-mass galaxies. Without this assumption, an overproduction of galaxies at the faint-end of the galaxy luminosity function seems inevitable in our models.

WIMP-nucleus scattering in chiral effective theory [Cross-Listing]

astro-ph — Tue, 15 May 2012 00:54:35 +0000

We discuss long-distance QCD corrections to the WIMP-nucleon(s) interactions in the framework of chiral effective theory. For scalar-mediated WIMP-quark interactions, we calculate all the next-to-leading-order corrections to the WIMP-nucleus elastic cross-section, including two-nucleon amplitudes and recoil-energy dependent shifts to the single-nucleon scalar form factors. As a consequence, the scalar-mediated WIMP-nucleus cross-section cannot be parameterized in terms of just two quantities, namely the neutron and proton scalar form factors at zero momentum transfer, but additional parameters appear, depending on the short-distance WIMP-quark interaction. Moreover, multiplicative factorization of the cross-section into particle, nuclear and astro-particle parts is violated. In practice, while the new effects are of the natural size expected by chiral power counting, they become very important in those regions of parameter space where the leading order WIMP-nucleus amplitude is suppressed, including the so-called “isospin-violating dark matter” regime. In these regions of parameter space we find order-of-magnitude corrections to the total scattering rates and qualitative changes to the shape of recoil spectra.

Large Scale Structure in Absorption: Gas within and around Galaxy Voids

astro-ph — Tue, 15 May 2012 00:54:15 +0000

We investigate the properties of the HI Ly-a absorption systems (Ly-a forest) within and around galaxy voids at z99% c.l.) of Ly-a systems at the edges of galaxy voids with respect to a random distribution, on ~5 h^{-1} Mpc scales. We find no significant difference in the number of systems inside voids with respect to the random expectation. We report differences between both column density (N_{HI}) and Doppler parameter (b_{HI}) distributions of Ly-a systems found inside and at the edge of galaxy voids at the >98% and >90% c.l. respectively. Low density environments (voids) have smaller values for both N_{HI} and b_{HI} than higher density ones (edges of voids). These trends are theoretically expected and also found in GIMIC, a state-of-the-art hydrodynamical simulation. Our findings are consistent with a scenario of at least three types of Ly-alpha: (1) containing embedded galaxies and so directly correlated with galaxies (referred as `halo-like’), (2) correlated with galaxies only because they lie in the same over-dense LSS, and (3) associated with under-dense LSS with a very low auto-correlation amplitude (~ random) that are not correlated with luminous galaxies. We argue the latter arise in structures still growing linearly from the primordial density fluctuations inside galaxy voids that have not formed galaxies because of their low densities. We estimate that these under-dense LSS absorbers account for 25-30% +- 6% of the current Ly-a population (N_{HI} > 10^{12.5} cm^{-2}) while the other two types account for the remaining 70-75% +- 12%. Assuming that only N_{HI} > 10^{14} cm^{-2} systems have embedded galaxies nearby, we have estimated the contribution of the `halo-like’ Ly-a to be ~12-15% +- 4% and consequently ~55-60% +- 13% of the Ly-a systems to be associated with the over-dense LSS.

Redshift space distortions in f(R) gravity

astro-ph — Tue, 15 May 2012 00:53:56 +0000

We use large volume, high resolution N-body simulations to predict the clustering of dark matter in redshift space in f(R) modified gravity cosmologies. This is the first time that the nonlinear matter and velocity fields have been resolved to such a high level of accuracy over a broad range of scales in this class of models. We find significant deviations from the clustering signal in standard gravity, with an enhanced boost in power on large scales and stronger damping on small scales in the f(R) models compared to GR at redshifts z<1. We measure the velocity divergence (P_\theta \theta) and matter (P_\delta \delta) power spectra and find a large deviation in the ratios \sqrt{P_\theta \theta/P_\delta \delta} and P_\delta \theta/P_\delta\delta, between the f(R) models and GR for 0.03

A cosmological view of extreme mass-ratio inspirals in nuclear star clusters

astro-ph — Tue, 15 May 2012 00:53:33 +0000

There is increasing evidence that many galaxies host both a nuclear star cluster (NC) and a super-massive black hole (SMBH). Their coexistence is particularly prevalent in spheroids with stellar mass 10^8-10^10 solar masses. We study the possibility that a stellar-mass black hole (BH) hosted by a NC inspirals and merges with the central SMBH. Due to the high stellar density in NCs, extreme mass-ratio inspirals (EMRIs) of BHs onto SMBHs in NCs may be important sources of gravitational waves (GWs). We consider sensitivity curves for three different space-based GW laser interferometric mission concepts: the Laser Interferometer Space Antenna (LISA), the New Gravitational wave Observatory (NGO) and the DECi-hertz Interferometer Gravitational wave Observatory (DECIGO). We predict that, under the most optimistic assumptions, LISA and DECIGO will detect up to thousands of EMRIs in NCs per year, while NGO will observe up to tens of EMRIs per year. We explore how a number of factors may affect the predicted rates. In particular, if we assume that the mass of the SMBH scales with the square of the host spheroid mass in galaxies with NCs, rather than a linear scaling, then the event rates are more than a factor of 10 lower for both LISA and NGO, while they are almost unaffected in the case of DECIGO.

A wide-area view of the Phoenix dwarf galaxy from VLT/FORS imaging

astro-ph — Tue, 15 May 2012 00:53:01 +0000

We present results from a wide-area photometric survey of the Phoenix dwarf galaxy, one of the rare dwarf irregular/ dwarf spheroidal transition type galaxies (dTs) of the Local Group (LG). These objects offer the opportunity to study the existence of possible evolutionary links between the late- and early- type LG dwarf galaxies, since the properties of dTs suggest that they may be dwarf irregulars in the process of transforming into dwarf spheroidals. Using FORS at the VLT we have acquired VI photometry of Phoenix. The data reach a S/N~10 just below the horizontal branch of the system and consist of a mosaic of images that covers an area of 26′ x 26′ centered on the coordinates of the optical center of the galaxy. Examination of the colour-magnitude diagram and luminosity function revealed the presence of a bump above the red clump, consistent with being a red giant branch bump. The deep photometry combined with the large area covered allows us to put on a secure ground the determination of the overall structural properties of the galaxy and to derive the spatial distribution of stars in different evolutionary phases and age ranges, from 0.1 Gyr to the oldest stars. The best-fitting profile to the overall stellar population is a Sersic profile of Sersic radius R_S = 1.82′+-0.06′ and m=0.83+-0.03. We confirm that the spatial distribution of stars is found to become more and more centrally concentrated the younger the stellar population, as reported in previous studies. This is similar to the stellar population gradients found for close-by Milky Way dwarf spheroidal galaxies. We quantify such spatial variations by analyzing the surface number density profiles of stellar populations in different age ranges; [Abridged]

A New Method to Constrain Supernova Fractions Using X-ray Observations of Clusters of Galaxies

astro-ph — Tue, 15 May 2012 00:52:07 +0000

Supernova (SN) explosions enrich the intra-cluster medium (ICM) both by creating and dispersing metals. We introduce a method to measure the number of SNe and relative contribution of Type Ia supernovae (SNe Ia) and core-collapse supernovae (SNe cc) by directly fitting X-ray spectral observations. The method has been implemented as an XSPEC model called snapec. snapec utilizes a single temperature thermal plasma code (apec) to model the spectral emission based on metal abundances calculated using the latest SN yields from SN Ia and SN cc explosion models. This approach provides a self-consistent single set of uncertainties on the total number of SN explosions and relative fraction of SN types in the ICM over the cluster lifetime by directly allowing these parameters to be determined by SN yields provided by simulations. We apply our approach to the XMM-Newton European Photon Imaging Camera (EPIC), Reflection Grating Spectrometer (RGS), and 200 ks simulated Astro-H observations of a cooling flow cluster, A3112. We find that various sets of SN yields present in the literature produce an acceptable fit to the EPIC and RGS spectra of A3112. We infer that 30.3% +/- 5.4% of the total SN explosions are SNe Ia, and the total number of SN explosions required to create the observed metals is in the order of (1.06 +/- 0.34)*10^{9}, from snapec fits to RGS spectra. These values may be compared to the enrichment expected based on well-established empirically-measured SN rates per star formed. The proportions of SNe Ia and SNe cc inferred to have enriched the ICM in the inner 52 kpc of A3112 is consistent with these specific rates, if one applies a correction for the metals locked up in stars. At the same time, the inferred level of SN enrichment corresponds to a star-to-gas mass ratio that is several times greater than the 10% estimated globally for clusters in the A3112 mass range.

An Efficient Parameter Space Search as an Alternative to Markov Chain Monte Carlo

astro-ph — Tue, 15 May 2012 00:51:53 +0000

We consider the problem of inferring constraints on a high-dimensional parameter space with a computationally expensive likelihood function. Markov chain Monte Carlo (MCMC) methods offer significant improvements in efficiency over grid-based searches and are easy to implement in a wide range of cases. However, MCMCs offer few guarantees that all of the interesting regions of parameter space are explored. We propose a machine learning algorithm that improves upon the performance of MCMC by intelligently targeting likelihood evaluations so as to quickly and accurately characterize the likelihood surface in both low- and high-likelihood regions. We compare our algorithm to MCMC on toy examples and the 7-year WMAP cosmic microwave background data release. Our algorithm finds comparable parameter constraints to MCMC in fewer calls to the likelihood function and with greater certainty that all of the interesting regions of parameter space have been explored.

The Cosmic Spacetime [Cross-Listing]

astro-ph — Tue, 15 May 2012 00:51:40 +0000

Cosmology today is confronted with several seemingly insoluble puzzles and strange, inexplicable coincidences. But a careful re-examination of the Cosmological principle and the Weyl postulate, foundational elements in this subject, suggests that we may be missing the point. The observations actually reveal a simpler and more elegant Universe than anyone could have imagined.

Formation of Galactic Pseudo-bulges via Gas Rich Major Mergers

astro-ph — Tue, 15 May 2012 00:51:23 +0000

It is widely accepted that within the framework of LCDM a significant fraction of giant-disk galaxies has recently experienced a violent galactic merger. We present numerical simulations of such major mergers of gas-rich pure disk galaxies, and focus on the innermost stellar component (bulge) of the disk remnants. The simulations have high spatial and mass resolutions, and resolve regions deep enough to allow bulge classification according to standard kinematical and structural characteristics. In agreement with recent studies we find that these bulges are dominated by stars formed in the final coalescence process. In contrast to the common interpretation of such components as classical bulges (i.e. similar to intermediate luminosity ellipticals), we find they are supported by highly coherent rotations and have Sersic indices n<2, a result leading to their classification as pseudo-bulges. Pseudo-bulge formation by gas rich major mergers of pure disks is a novel mode of pseudo-bulge formation; It complements pseudo-bulge growth by secular evolution, and it could help explain the high fractions of classically bulge-less giant disk galaxies, and pseudo-bulges found in giant Sc galaxies.

Gravitational softening as a smoothing operation

astro-ph — Tue, 15 May 2012 00:50:49 +0000

In self-consistent N-body simulations of collisionless systems, gravitational interactions are modified on small scales to remove singularities and simplify the task of numerically integrating the equations of motion. This `gravitational softening’ is sometimes presented as an ad-hoc departure from Newtonian gravity. However, softening can also be described as a smoothing operation applied to the mass distribution; the gravitational potential and the smoothed density obey Poisson’s equation precisely. While `softening’ and `smoothing’ are mathematically equivalent descriptions, the latter has some advantages. For example, the smoothing description suggests a way to set up N-body initial conditions in almost perfect dynamical equilibrium.

Observational Constraints on the Molecular Gas Content in Nearby Starburst Dwarf Galaxies

astro-ph — Tue, 15 May 2012 00:50:28 +0000

Using star formation histories derived from optically resolved stellar populations in nineteen nearby starburst dwarf galaxies observed with the Hubble Space Telescope, we measure the stellar mass surface densities of stars newly formed in the bursts. By assuming a star formation efficiency (SFE), we then calculate the inferred gas surface densities present at the onset of the starbursts. Assuming a SFE of 1%, as is often assumed in normal star-forming galaxies, and assuming that the gas was purely atomic, translates to very high HI surface densities (~10^2-10^3 Msun pc^-2), which are much higher than have been observed in dwarf galaxies. This implies either higher values of SFE in these dwarf starburst galaxies or the presence of significant amounts of H_2 in dwarfs (or both). Raising the assumed SFEs to 10% or greater (in line with observations of more massive starbursts associated with merging galaxies), still results in HI surface densities higher than observed in 10 galaxies. Thus, these observations appear to require that a significant fraction of the gas in these dwarf starbursts galaxies was in the molecular form at the onset of the bursts. Our results imply molecular gas column densities in the range 10^19-10^21 cm^-2 for the sample. In those galaxies where CO observations have been made, these densities correspond to values of the CO-H_2 conversion factor (X_CO) in the range >3-80×10^20 cm^-2 (K km s^-1)^-1, or up to 40x greater than Galactic X_CO values.

Non-Gaussianities in the Cosmological Perturbation Spectrum due to Primordial Anisotropy II

astro-ph — Tue, 15 May 2012 00:48:48 +0000

We continue to investigate possible signatures of a pre-inflationary anisotropic phase in two-point and three point correlation functions of the curvature perturbation for high-momentum modes which exit the horizon well after isotropization. The late time dynamics of these modes is characterized by a non-Bunch Davies vacuum state which encodes all the information about initial anisotropy in the background space-time. We observe that, unlike the non-planar momenta, there exist regimes of planar momenta for which scale invariance of the power spectrum is strongly broken. This regime of planar momenta gives rise to enhanced non-Gaussianity in certain squeezed triangle configurations, although the enhancement of the $f_{NL}$ parameter is limited by the breakdown of linear perturbation theory at “exact planarity”. Finally, we demonstrate that for the range of planar modes for which scale invariance of the power spectrum is preserved, non-Gaussianity in the curvature perturbation spectrum is naturally constrained to be extremely small.

Primordial Non-Gaussianity in the Forest: 3D Bispectrum of Ly-alpha Flux Spectra Along Multiple Lines of Sight

astro-ph — Tue, 15 May 2012 00:47:24 +0000

We investigate the possibility of constraining primordial non-Gaussianity using the 3D bispectrum of Ly-alpha forest. The strength of the quadratic non-Gaussian correction to an otherwise Gaussian primordial gravitational field is assumed to be dictated by a single parameter fnl. We present the first prediction for bounds on fnl using Ly-alpha flux spectra along multiple lines of sight. The 3D Ly-$\alpha$ transmitted flux field is modeled as a biased tracer of the underlying matter distribution sampled along 1D skewers corresponding to quasars sight lines. The precision to which fnl can be constrained depends on the survey volume, pixel noise and aliasing noise (arising from discrete sampling of the density field). We consider various combinations of these factors to predict bounds on fnl. We find that in an idealized situation of full sky survey and negligible Poisson noise one may constrain fnl ~ 23 in the equilateral limit. Assuming a Ly-alpha survey covering large parts of the sky (k_{min} = 8 * 10^{-4} Mpc^{-1}) and with a quasar density of \bar n = 5 * 10^{-3} Mpc^{-2} it is possible to constrain fnl ~ 100 for equilateral configurations. The possibility of measuring fnl at a precision comparable to LSS studies maybe useful for joint constraining of inflationary scenarios using different data sets.

Spatially-resolved HST Grism Spectroscopy of a Lensed Emission Line Galaxy at z~1

astro-ph — Tue, 15 May 2012 00:46:58 +0000

We take advantage of gravitational lensing amplification by Abell 1689 (z=0.187) to undertake the first space-based census of emission line galaxies (ELGs) in the field of a massive lensing cluster. Forty-three ELGs are identified to a flux of i_775=27.3 via slitless grism spectroscopy. One ELG (at z=0.7895) is very bright owing to lensing magnification by a factor of ~4.5. Several Balmer emission lines detected from ground-based follow-up spectroscopy signal the onset of a major starburst for this low-mass galaxy (M_* = 2 x 10^9 solar masses) with a high specific star formation rate (~20 /Gyr). From the blue emission lines we measure a gas-phase oxygen abundance consistent with solar (12+log(O/H)=8.8 +/- 0.2). We break the continuous line-emitting region of this giant arc into seven ~1kpc bins (intrinsic size) and measure a variety of metallicity dependent line ratios. A weak trend of increasing metal fraction is seen toward the dynamical center of the galaxy. Interestingly, the metal line ratios in a region offset from the center by ~1kpc have a placement on the blue HII region excitation diagram with f([OIII])/f(Hbeta) and f([NeIII])/f(Hbeta) that can be fit by an AGN. This asymmetrical AGN-like behavior is interpreted as a product of shocks in the direction of the galaxy’s extended tail, possibly instigated by a recent galaxy interaction.

Observational Constraints on Modified Chaplygin Gas in Horava-Lifshitz Gravity

astro-ph — Tue, 15 May 2012 00:46:46 +0000

We present Cosmological models with modified Chaplygin gas (MCG) in the framework of Horava-Lifshitz (HL) theory of gravity both with and without detailed balance. The equation of state (EOS) for a MCG contains three unknown parameters namely, $A$, $\alpha$, $B$. The allowed values of some of these parameters of the EOS are determined using the recent astrophysical and cosmological observational data. Using observational data from $H(z)-z$, BAO peak parameter, CMB shift parameter we study cosmologies in detailed-balance and beyond detailed-balance scenario. In this paper we take up the beyond detailed-balance scenario in totality and contribution of dark radiation in the case of detailed-balance scenario on the parameters of the EOS. We explore the effect of dark radiation on the whole range the of effective neutrino parameter to constrain matter contributing parameter $B$ in both the detailed-balance and the beyond-detailed balance scenario. It has been observed that greater the dark radiation less the matter contribution in the MCG in both the scenario considered here. In order to check the validity of beyond detailed balance scenario we plot supernovae magnitudes ($\mu$) with redshift of Union2 data and then the variation of state parameter with redshift is studied. It has been observed that beyond detailed balance scenario is equally suitable in HL gravity with MCG.

Relativistic Solution for a Class of Static Compact Charged Star in Pseudo Spheroidal Space-Time

astro-ph — Tue, 15 May 2012 00:46:34 +0000

Considering Vaidya-Tikekar metric, we obtain a class of solutions of the Einstein-Maxwell equations for a charged static fluid sphere. The physical 3-space (t=constant) here is described by pseudo-spheroidal geometry. The relativistic solution for the theory is used to obtain models for charged compact objects, thereafter a qualitative analysis of the physical aspects of compact objects are studied. The dependence of some of the properties of a superdense star on the parameters of the three geometry is explored. We note that the spheroidicity parameter $a$, plays an important role for determining the properties of a compact object. A non-linear equation of state is required to describe a charged compact object with pseudo-spheroidal geometry which we have shown for known masses of compact objects. We also note that the size of a static compact charged star is more than that of a static compact star without charge.

Probing the Supersymmetric Inflaton and Dark Matter link via the CMB, LHC and XENON1T experiments [Cross-Listing]

astro-ph — Tue, 15 May 2012 00:46:13 +0000

The primordial inflation dilutes all matter except the quantum fluctuations which we see in the cosmic microwave background (CMB) radiation. Therefore the last phases of inflation must be embedded within a beyond the Standard Model (SM) sector where the inflaton can directly excite the SM quarks and leptons. In this paper we consider two inflaton candidates LLe and udd whose decay can naturally excite all the relevant degrees of freedom besides thermalizing the lightest supersymmetric particle (LSP) during and after reheating. In particular, we present the regions of the parameter space which can yield successful inflation with the right temperature anisotropy in the CMB, the observed relic density for the neutralino LSP, and the recent Higgs mass constraints from LHC within the MSSM with non-universal Higgs masses — referred to as the NUHM2 model. We found that in most scenarios, the LSP seems strongly mass degenerated with the next to lightest LSP (NLSP) and the branching ratio B_s -> mu^+ mu^- very close to the present bound, thus leading to falsifiable predictions. Also the dark matter interactions with XENON nuclei would fall within the projected range for the XENON1T experiment. In the case of a positive signal of low scale supersymmetry at the LHC, one would be able to potentially pin down the inflaton mass by using the associated values for the mass of the stau, the stop and the neutralino.

Originally Asymmetric Dark Matter [Cross-Listing]

astro-ph — Tue, 15 May 2012 00:45:52 +0000

We propose a scenario with a fermion dark matter, where the dark matter particle used to be the Dirac fermion, but it takes the form of the Majorana fermion at a late time. The relic number density of the dark matter is determined by the dark matter asymmetry generated through the same mechanism as leptogenesis when the dark matter was the Dirac fermion. After efficient dark matter annihilation processes have frozen out, a phase transition of a scalar field takes place and generates Majorana mass terms to turn the dark matter particle into the Majorana fermion. In order to address this scenario in detail, we propose two simple models. The first one is based on the Standard Model (SM) gauge group and the dark matter originates the $SU(2)_L$ doublet Dirac fermion, analogous to the Higgsino-like neutralino in supersymmetric models. We estimate the spin-independent/dependent elastic scattering cross sections of this late-time Majorana dark matter with a proton and find the possibility to discover it by the direct and/or indirect dark matter search experiments in the near future. The second model is based on the $B-L$ gauged extension of the SM, where the dark matter is a SM singlet. Although this model is similar to the so-called Higgs portal dark matter scenario, the spin-independent elastic scattering cross section can be large enough to detect this dark matter in future experiments.

A new null diagnostic customized for reconstructing the properties of dark energy from BAO data

astro-ph — Tue, 15 May 2012 00:45:19 +0000

Baryon Acoustic Oscillations (BAO) provide an important standard ruler which can be used to probe the recent expansion history of our universe. We show how a simple extension of the Om diagnostic, which we call Om3, can combine standard ruler information from BAO with standard candle information from type Ia supernovae (SNIa) to yield a powerful novel null diagnostic of the cosmological constant hypothesis. A unique feature of Om3 is that it requires minimal cosmological assumptions since its determination does not rely upon prior knowledge of either the current value of the matter density and the Hubble constant, or the distance to the last scattering surface. Observational uncertainties in these quantities therefore do not affect the reconstruction of Om3. We reconstruct Om3 using the Union 2.1 SNIa data set and BAO data from SDSS, WiggleZ and 6dFGS. Our results are consistent with dark energy being the cosmological constant. We show how Om and Om3 can be used to obtain accurate model independent constraints on the properties of dark energy from future data sets such as BigBOSS.

Mixing of blackbodies: entropy production and dissipation of sound waves in the early Universe

astro-ph — Tue, 15 May 2012 00:45:06 +0000

Mixing of blackbodies with different temperatures creates a spectral distortion which, at lowest order, is a y-type distortion, indistinguishable from the thermal y-type distortion produced by the scattering of CMB photons by hot electrons residing in clusters of galaxies. This process occurs in the radiation-pressure dominated early Universe, when the primordial perturbations excite standing sound waves on entering the sound horizon. Photons from different phases of the sound waves, having different temperatures, diffuse through the electron-baryon plasma and mix together. This diffusion, with the length defined by Thomson scattering, dissipates sound waves and creates spectral distortions in the CMB. Of the total dissipated energy, 2/3 raises the average temperature of the blackbody part of spectrum, while 1/3 creates a distortion of y-type. It is well known that at redshifts 10^5< z< 2×10^6, comptonization rapidly transforms y-distortions into a Bose-Einstein spectrum. The chemical potential of the Bose-Einstein spectrum is again 1/3 the value we would get if all the dissipated energy was injected into a blackbody spectrum but no extra photons were added. We study the mixing of blackbody spectra, emphasizing the thermodynamic point of view, and identifying spectral distortions with entropy creation. This allows us to obtain the main results connected with the dissipation of sound waves in the early Universe in a very simple way. We also show that mixing of blackbodies in general, and dissipation of sound waves in particular, leads to creation of entropy.