Vox Charta » astro-ph

http://xxx.lanl.gov/pdf/1202.0478.pdf

EG — Fri, 03 Feb 2012 04:21:54 +0000

Dust Attenuation and H-alpha Star Formation Rates of z~0.5 Galaxies

astro-ph — Fri, 03 Feb 2012 01:58:27 +0000

Using deep narrow-band and broad-band imaging, we identify 401 z~0.40 and 249 z~0.49 H-alpha line-emitting galaxies in the Subaru Deep Field. Compared to other H-alpha surveys at similar redshifts, our samples are unique since they probe lower H-alpha luminosities, are augmented with multi-wavelength (rest-frame 1000AA–1.5 microns) coverage, and a large fraction (20%) of our samples has already been spectroscopically confirmed. Our spectra allow us to measure the Balmer decrement for nearly 60 galaxies with H-beta detected above 5-sigma. The Balmer decrements indicate an average extinction of A(H-alpha)=0.7^{+1.4}_{-0.7} mag. We find that the Balmer decrement systematically increases with higher H-alpha luminosities and with larger stellar masses, in agreement with previous studies with sparser samples. We find that the SFRs estimated from modeling the spectral energy distribution (SED) is reliable—we derived an “intrinsic” H-alpha luminosity which is then reddened assuming the color excess from SED modeling. The SED-predicted H-alpha luminosity agrees with H-alpha narrow-band measurements over 3 dex (rms of 0.25 dex). We then use the SED SFRs to test different statistically-based dust corrections for H-alpha and find that adopting one magnitude of extinction is inappropriate: galaxies with lower luminosities are less reddened. We find that the luminosity-dependent dust correction of Hopkins et al. yields consistent results over 3 dex (rms of 0.3 dex). Our comparisons are only possible by assuming that stellar reddening is roughly half of nebular reddening. The strong correspondence argue that with SED modeling, we can derive reliable intrinsic SFRs even in the absence of H-alpha measurements at z~0.5.

Dust to Dust: 3 years in the Evolution of the Unusual SN 2008S

astro-ph — Fri, 03 Feb 2012 01:58:04 +0000

We obtained late-time optical and near-IR imaging of SN 2008S with the Large Binocular Telescope (LBT), near-IR data with the Hubble Space Telescope (HST), and mid-IR data with the Spitzer Space Telescope (SST). We find that (1) it is again invisible at optical (UBVR) wavelengths to magnitude limits of approximately 25 mag, (2) while detected in the near-IR (H) at approximately 24.8 mag, it is fading rapidly, and (3) it is still brighter than the progenitor at 3.6 and 4.5 microns in the mid-IR with a slow, steady decline. The IR detections in December 2010 are consistent with dust emission at a blackbody temperature of T ~ 640 K and a total luminosity of L ~ 200000 Lsun, much higher than the L ~ 40000 Lsun luminosity of the obscured progenitor star. The local environment also shows no evidence for massive (M >= 10 Msun) stars in the vicinity of the transient, consistent with the progenitor being a massive AGB star.

Discovery of a compact gas-rich DLA galaxy at z = 2.2: evidences for a starburst-driven outflow

astro-ph — Fri, 03 Feb 2012 01:57:49 +0000

We present the detection of Ly-alpha, [OIII] and H-alpha emission associated with an extremely strong DLA system (N(HI) = 10^22.10 cm^-2) at z=2.207 towards the quasar SDSS J113520-001053. This is the largest HI column density ever measured along a QSO line of sight, though typical of what is seen in GRB-DLAs. This absorption system also classifies as ultrastrong MgII system with W2796_r=3.6 A. The mean metallicity of the gas ([Zn/H]=-1.1) and dust depletion factors ([Zn/Fe]=0.72, [Zn/Cr]=0.49) are consistent with (and only marginally larger than) the mean values found in the general QSO-DLA population. The [OIII]-Ha emitting region has a very small impact parameter with respect to the QSO line of sight, b=0.1″, and is unresolved. From the Ha line, we measure SFR=25 Msun/yr. The Ly-a line is double-peaked and is spatially extended. More strikingly, the blue and red Ly-a peaks arise from distinct regions extended over a few kpc on either side of the star-forming region. We propose that this is the consequence of Ly-a transfer in outflowing gas. The presence of starburst-driven outflows is also in agreement with the large SFR together with a small size and low mass of the galaxy (Mvir~10^10 Msun). From the stellar UV continuum luminosity of the galaxy, we estimate an age of at most a few 10^7 yr, again consistent with a recent starburst scenario. We interpret the data as the observation of a young, gas rich, compact starburst galaxy, from which material is expelled through collimated winds powered by the vigorous star formation activity. We substantiate this picture by modelling the radiative transfer of Ly-a photons in the galactic counterpart. Though our model (a spherical galaxy with bipolar outflowing jets) is a simplistic representation of the true gas distribution and velocity field, the agreement between the observed and simulated properties is particularly good. [abridged]

Unmasking the Supernova Impostors

astro-ph — Fri, 03 Feb 2012 01:57:34 +0000

(ABRIDGED) The canonical picture of a supernova impostor is a -11 < M_V 40Msun) star during which the star ejects a dense shell of material. Dust formed in the ejecta then obscures the star. In this picture, the geometric expansion of the shell leads to clear predictions for the evolution of the optical depths and hence the evolution of the optical through mid-IR emissions. Here we review the theory of this standard model and then examine the impostors SN1954J, SN1997bs, SN1999bw, SN2000ch, SN2001ac, SN2002bu, SN2002kg and SN2003gm, as well as the potential archetype eta Carinae. SN1999bw, SN2000ch, SN2001ac, SN2002bu and SN2003gm all show mid-IR emission indicative of dust, and the luminosities of SN1999bw, SN2001ac, SN2002bu and SN2003gm are dominated by dust emission. The properties of these sources are broadly inconsistent with the predictions of the canonical model. There are probably two classes of sources. In one class (eta Carinae, SN1954J, SN1997bs, and (maybe) SN2003gm), the optical transient is a signal that the star is entering a phase with very high mass loss rates that must last far longer than the visual transient. The second class (SN1999bw, SN2001ac, SN2002bu and (maybe) SN2003gm) has the different physics of SN2008S and the 2008 NGC300 transient, where they are obscured by dust re-forming in a pre-existing wind after it was destroyed by an explosive transient. There are no cases where the source at late times is significantly fainter than the progenitor star. All these dusty transients are occurring in relatively low mass (M 40Msun) stars radiating near the Eddington limit like eta Carinae. The durations and energetics of these transients cannot be properly characterized without near/mid-IR observations.

Energetic feedback and $^{26}$Al from massive stars and their supernovae in the Carina region

astro-ph — Fri, 03 Feb 2012 01:57:10 +0000

We study the populations of massive stars in the Carina region and their energetic feedback and ejection of $^{26}$Al. We did a census of the stellar populations in young stellar clusters within a few degrees of the Carina Nebula. For each star we estimated the mass, based on the spectral type and the host cluster age. We used population synthesis to calculate the energetic feedback and ejection of $^{26}$Al from the winds of the massive stars and their supernova explosions. We used 7 years of INTEGRAL observations to measure the $^{26}$Al signal from the region. The INTEGRAL $^{26}$Al signal is not significant with a best-fit value of about 1.5e-5 ph/cm^2/s, approximately half of the published Compton Gamma Ray Observatory (CGRO) result, but in agreement with the latest CGRO estimates. Our analysis of the stellar populations in the young clusters leads to an expected signal of half the observed value, but the results are consistent within 2 sigma. We find that the fraction of $^{26}$Al ejected in Wolf-Rayet winds is high, and the observed signal is unlikely to be caused by $^{26}$Al ejected in supernovae alone, indicating a strong wind ejection of $^{26}$Al. Due to the lack of prominent O stars, regions with ages $\gtrsim$10 Myr are often neglected in studies of OB associations. We find that in the Carina region such clusters contribute significantly to the stellar mass and the energetics of the region.

Oscillating Asymmetric Dark Matter [Cross-Listing]

astro-ph — Fri, 03 Feb 2012 01:56:56 +0000

We study the dynamics of dark matter (DM) particle-antiparticle oscillations within the context of asymmetric DM. Oscillations arise due to small DM number-violating Majorana-type mass terms, and can lead to recoupling of annihilation after freeze-out and washout of the DM density. We derive the density matrix equations for DM oscillations and freeze-out from first principles using nonequilibrium field theory, and our results are qualitatively different than in previous studies. DM dynamics exhibits particle-vs-antiparticle “flavor” effects, depending on the interaction type, analogous to neutrino oscillations in a medium. “Flavor-sensitive” DM interactions include scattering or annihilation through a new vector boson, while “flavor-blind” interactions include scattering or s-channel annihilation through a new scalar boson, or annihilation to pairs of bosons. In particular, we find that flavor-sensitive annihilation does not recouple when coherent oscillations begin, and that flavor-blind scattering does not lead to decoherence.

Cosmography from two-image lens systems: overcoming the lens profile slope degeneracy

astro-ph — Fri, 03 Feb 2012 01:56:12 +0000

The time delays between the multiple images of a strong lens system, together with a model of the lens mass distribution, allow a one-step measurement of a cosmological distance, namely, the “time-delay distance” of the lens (D_dt) that encodes cosmological information. The time-delay distance depends sensitively on the radial profile slope of the lens mass distribution; consequently, the lens slope must be accurately constrained for cosmological studies. We show that the slope cannot be constrained in two-image systems with single-component compact sources, whereas it can be constrained in systems with two-component sources provided the separation between the image components can be measured with milliarcsecond precisions, which is not feasible in most systems. In contrast, we demonstrate that spatially extended images of the source galaxy in two-image systems break the radial slope degeneracy and allow D_dt to be measured with uncertainties of a few percent. Deep and high-resolution imaging of the lens systems are needed to reveal the extended arcs, and stable point spread functions are required for our lens modelling technique. Two-image systems, no longer plagued by the radial profile slope degeneracy, would augment the sample of useful time-delay lenses by a factor of ~6, providing substantial advances for cosmological studies.

Inflation and dark matter in two Higgs doublet models [Cross-Listing]

astro-ph — Fri, 03 Feb 2012 01:55:50 +0000

We consider the Higgs inflation in the extension of the Standard Model with two Higgs doublets coupled to gravity non-minimally. In the presence of an approximate global U(1) symmetry in the Higgs sector, both radial and angular modes of neutral Higgs bosons drive inflation where large non-Gaussianity is possible from appropriate initial conditions on the angular mode. We also discuss the case with single-field inflation for which the U(1) symmetry is broken to a Z_2 subgroup. We show that inflationary constraints, perturbativity and stability conditions restrict the parameter space of the Higgs quartic couplings at low energy in both multi- and single-field cases. Focusing on the inert doublet models where Z_2 symmetry remains unbroken at low energy, we show that the extra neutral Higgs boson can be a dark matter candidate consistent with the inflationary constraints. The doublet dark matter is always heavy in multi-field inflation while it can be light due to the suppression of the co-annihilation in single-field inflation. The implication of the extra quartic couplings on the vacuum stability bound is also discussed in the light of the recent LHC limits on the Higgs mass.

The contribution of starbursts and normal galaxies to infrared luminosity functions at z < 2

astro-ph — Fri, 03 Feb 2012 01:55:29 +0000

We present a parameter-less approach to predict the shape of the infrared (IR) luminosity function (LF) at redshifts z < 2. It requires no tuning and relies on only three observables: (1) the redshift evolution of the stellar mass function for star-forming galaxies, (2) the evolution of the specific star formation rate (sSFR) of main-sequence galaxies, and (3) the double-Gaussian decomposition of the sSFR-distribution at fixed stellar mass into a contribution (assumed redshift- and mass-invariant) from main-sequence and starburst activity. This self-consistent and simple framework provides a powerful tool for predicting cosmological observables: observed IR LFs are successfully matched at all z < 2, suggesting a constant or only weakly redshift-dependent contribution (8-14%) of starbursts to the star formation rate density. We separate the contributions of main-sequence and starburst activity to the global IR LF at all redshifts. The luminosity threshold above which the starburst component dominates the IR LF rises from log(LIR/Lsun) = 11.4 to 12.8 over 0 < z < 2, reflecting our assumed (1+z)^2.8-evolution of sSFR in main-sequence galaxies.

Bayesian analysis of polarization measurements

astro-ph — Fri, 03 Feb 2012 01:55:15 +0000

A detailed and formal account of polarization measurements using Bayesian analysis is given based on the assumption of gaussian error for the Stokes parameters. This analysis is crucial for the measurement of the polarization degree and angle at very low (and very high) signal-to-noise. The treatment serves as a framework for customized analysis of data based on a particular prior suited to the experiment.

Precise Infrared Radial Velocities from Keck/NIRSPEC and the Search for Young Planets

astro-ph — Fri, 03 Feb 2012 01:54:43 +0000

We present a high-precision infrared radial velocity study of late-type stars using spectra obtained with NIRSPEC at the W. M. Keck Observatory. Radial velocity precisions of 50 m/s are achieved for old field mid-M dwarfs using telluric features for precise wavelength calibration. Using this technique, 20 young stars in the {\beta} Pic (age ~12 Myr) and TW Hya (age ~8 Myr) Associations were monitored over several years to search for low mass companions; we also included the chromospherically active field star GJ 873 (EV Lac) in this survey. Based on comparisons with previous optical observations of these young active stars, radial velocity measurements at infrared wavelengths mitigate the radial velocity noise caused by star spots by a factor of ~3. Nevertheless, star spot noise is still the dominant source of measurement error for young stars at 2.3 {\mu}m, and limits the precision to ~77 m/s for the slowest rotating stars (v sin i 12 km/s). The observations reveal both GJ 3305 and TWA 23 to be single-lined spectroscopic binaries; in the case of GJ 3305, the motion is likely caused by its 0.09″ companion, identified after this survey began. The large amplitude, short-timescale variations of TWA 13A are indicative of a hot Jupiter-like companion, but the available data are insufficient to confirm this. We label it as a candidate radial velocity variable. For the remainder of the sample, these observations exclude the presence of any ‘hot’ (P < 3 days) companions more massive than 8 MJup, and any 'warm' (P < 30 days) companions more massive than 17 MJup, on average. Assuming an edge-on orbit for the edge-on disk system AU Mic, these observations exclude the presence of any hot Jupiters more massive than 1.8 MJup or warm Jupiters more massive than 3.9 MJup.

Bayesian Analysis of Inflation III: Slow Roll Reconstruction Using Model Selection

astro-ph — Fri, 03 Feb 2012 01:54:30 +0000

We implement Slow Roll Reconstruction — an optimal solution to the inverse problem for inflationary cosmology — within ModeCode, a publicly available solver for the inflationary dynamics. We obtain up-to-date constraints on the reconstructed inflationary potential, derived from the WMAP 7-year dataset and South Pole Telescope observations, combined with large scale structure data derived from SDSS Data Release 7. Using ModeCode in conjunction with the MultiNest sampler, we compute Bayesian evidence for the reconstructed potential at each order in the truncated slow roll hierarchy. We find that the data are well-described by the first two slow roll parameters, \epsilon and \eta, and that there is no need to include a nontrivial \xi parameter.

An Oxygen Abundance Gradient into the Outer Disk of M81

astro-ph — Fri, 03 Feb 2012 01:54:09 +0000

The extended HI disk and tidal tails of M81 present an interesting environment to study the effects of galaxy interaction on star formation and chemical evolution of the outer disk of a large spiral galaxy. We present H{\alpha} imaging of the outer disk of M81 and luminosities for 40 HII regions out to about 3 times the optical radius. We have also obtained MMT spectra for 21 HII regions out to more than twice the optical radius. We derive strong line oxygen abundances for all HII regions using R_{23} based and [NII]/[OII] based calibrations and electron temperature abundances for seven regions spanning a galactocentric distance between 5.7 and 32 kpc. We also comment on the abundances of HII regions near KDG 61 and the “tidal dwarf” candidate HoIX. Our results constitute the most radially extended metallicity study for M81 to date. With this extended data set, we find an overall oxygen abundance gradient of -0.013 dex/kpc over the entire radial range. This is significantly flatter than what has been found in previous studies which were limited to the optical disk. From our temperature based abundances, we find a gradient of -0.020 dex/kpc and present the possibility of a broken gradient from these data, but note the need to obtain more temperature based abundances at intermediate galactocentric distances (~10-20 kpc) to verify whether or not this may be the case. We discuss our main result of a rather flat gradient for M81 in the context of simulations and observations of abundance gradients in other galaxies. We find that the shallow abundance gradient of M81 is likely a result of the interaction history of this galaxy.

Neutrinos and cosmic rays

astro-ph — Fri, 03 Feb 2012 01:53:41 +0000

In this paper we review the status of the search for high-energy neutrinos from outside the solar system and discuss the implications for the origin and propagation of cosmic rays. Connections between neutrinos and gamma-rays are also discussed.

All Curled Up: A Numerical Investigation of Shock-Bubble Interactions and the Role of Vortices in Heating Galaxy Clusters

astro-ph — Fri, 03 Feb 2012 01:53:04 +0000

Jets from active galactic nuclei in the centers of galaxy clusters inflate cavities of low density relativistic plasma and drive shock and sound waves into the intracluster medium. When these waves overrun previously inflated cavities, they form a differentially rotating vortex through the Richtmyer-Meshkov instability. The dissipation of energy captured in the vortex can contribute to the feedback of energy into the atmospheres of cool core clusters. Using a series of hydrodynamic simulations we investigate the efficiency of this process: we calculate the kinetic energy in the vortex by decomposing the velocity field into its irrotational and solenoidal parts. Compared to the two-dimensional case, the 3-dimensional Richtmyer-Meshkov instability is about a factor of 2 more efficient. The energy in the vortex field for weak shocks is E_vortex ~ rho_ICM v_shock^2 V_bubble (with dependence on the geometry, density contrast, and shock width). For strong shocks, the vortex becomes dynamically unstable, quickly dissipating its energy via a turbulent cascade. We derive a number of diagnostics for observations and laboratory experiments of shock-bubble interactions, like the shock-vortex standoff distance, which can be used to derive lower limits on the Mach number. The differential rotation of the vortex field leads to viscous dissipation, which is sufficiently efficient to react to cluster cooling and to dissipate the vortex energy within the cooling radius of the cluster for a reasonable range of vortex parameters. For sufficiently large filling factors (of order a few percent or larger), this process could thus contribute significantly to AGN feedback in galaxy clusters.

On the Application of Wesenheit Function in Deriving Distance to Galactic Cepheids

astro-ph — Fri, 03 Feb 2012 01:52:52 +0000

In this work, we explore the possibility of using the Wesenheit function to derive individual distances to Galactic Cepheids, as the dispersion of the reddening free Wesenheit function is smaller than the optical period-luminosity (P-L) relation. When compared to the distances from various methods, the averaged differences between our results and published distances range from -0.061 to 0.009, suggesting that the Wesenheit function can be used to derive individual Cepheid distances. We have also constructed Galactic P-L relations and selected Wesenheit functions based on the derived distances. A by-product from this work is the derivation of Large Magellanic Cloud distance modulus when calibrating the Wesenheit function. It is found to be 18.531 \pm 0.043 mag.

The shallow-decay phase in both optical and x-ray afterglows of Swift GRB 090529A: Energy injection into a wind-type medium?

astro-ph — Fri, 03 Feb 2012 01:52:35 +0000

The energy injection model is usually proposed to interpret the shallow-decay phase in Swift GRB X-ray afterglows. However, very few GRBs have simultaneous signatures of energy injection in their optical and X-ray afterglows. Here, we report optical observations of GRB 090529A from 2000 sec to $\sim10^6$ sec after the burst, in which an achromatic decay is seen at both wavelengths. The optical light curve shows a decay from 0.37 to 0.99 with a break at $\sim10^5$ sec. In the same time interval, the decay indices of the X-ray light curve changed from 0.04 to 1.2. Comparing these values with the closure relations, the segment after 3$\times10^{4}$ sec is consistent with the prediction of the forward shock in an ISM medium without any energy injection. The shallow-decay phase between 2000 to 3$\times10^{4}$ sec could be due to the external shock in a wind-type-like medium with an energy injection under the condition of $\nu_o < \nu_c < \nu_x$. However, the constraint of the spectral region is not well consistent with the multi-band observations. For this shallow-decay phase, other models are also possible, such as energy injection with evolving microphysical parameters, or a jet viewed off-axis,etc.

Radiative Models of Sagittarius A* and M87 from Relativistic MHD Simulations

astro-ph — Fri, 03 Feb 2012 01:52:22 +0000

Ongoing millimeter VLBI observations with the Event Horizon Telescope allow unprecedented study of the innermost portion of black hole accretion flows. Interpreting the observations requires relativistic, time-dependent physical modeling. We discuss the comparison of radiative transfer calculations from general relativistic MHD simulations of Sagittarius A* and M87 with current and future mm-VLBI observations. This comparison allows estimates of the viewing geometry and physical conditions of the Sgr A* accretion flow. The viewing geometry for M87 is already constrained from observations of its large-scale jet, but, unlike Sgr A*, there is no consensus for its millimeter emission geometry or electron population. Despite this uncertainty, as long as the emission region is compact, robust predictions for the size of its jet launching region can be made. For both sources, the black hole shadow may be detected with future observations including ALMA and/or the LMT, which would constitute the first direct evidence for a black hole event horizon.

Inclusive Constraints on Unified Dark Matter Models from Future Large-Scale Surveys

astro-ph — Fri, 03 Feb 2012 01:52:04 +0000

In the very last years, cosmological models where the properties of the dark components of the Universe – dark matter and dark energy – are accounted for by a single “dark fluid” have drawn increasing attention and interest. Amongst many proposals, Unified Dark Matter (UDM) cosmologies are promising candidates as effective theories. In these models, a scalar field with a non-canonical kinetic term in its Lagrangian mimics both the accelerated expansion of the Universe at late times and the clustering properties of the large-scale structure of the cosmos. However, UDM models also present peculiar behaviours, the most interesting one being the fact that the perturbations in the dark-matter component of the scalar field do have a non-negligible speed of sound. This gives rise to an effective Jeans scale for the Newtonian potential, below which the dark fluid does not cluster any more. This implies a growth of structures fairly different from that of the concordance LCDM model. In this paper, we demonstrate that forthcoming large-scale surveys will be able to discriminate between viable UDM models and LCDM to a good degree of accuracy. To this purpose, the planned Euclid satellite will be a powerful tool, since it will provide very accurate data on galaxy clustering and the weak lensing effect of cosmic shear. Finally, we also exploit the constraining power of the ongoing CMB Planck experiment. Although our approach is the most conservative, with the inclusion of only well-understood, linear dynamics, in the end we also show what could be done if some amount of non-linear information were included.

The Local Volume HI Survey: Galaxy Kinematics

astro-ph — Fri, 03 Feb 2012 01:51:48 +0000

We present a detailed analysis of the neutral hydrogen kinematics of 12 nearby dwarf irregular galaxies observed as part of the Local Volume HI Survey (LVHIS) conducted at the Australia Telescope Compact Array. For each galaxy we measure the disk parameters (inclination, position angle) and the HI rotation curve. Six galaxies in our sample (AM0605-341, Argo Dwarf, ESO059-G001, ESO137-G018, ESO174-G?001, ESO308-G022) have their atomic hydrogen distribution studied for the first time. AM0605-341 was found to have an extension of redshifted HI which we propose is due to a tidal interaction with NGC2188. There is evidence that ESO215-G?009 has extraplanar HI gas. We also compare the global galaxy properties, in particular the integrated HI flux density and velocity widths of the observed HI spectra with the results from the low angular resolution HI Parkes All Sky Survey (HIPASS). We discuss under what circumstances the 21cm emission line profile can accurately predict the galaxy’s rotation velocity, an observational parameter crucial to study the classical and baryonic Tully-Fisher relations.

AstroParticle Physics at the Highest Energies

astro-ph — Fri, 03 Feb 2012 01:51:33 +0000

Recent international efforts have brought us closer to unveiling the century old mystery of the origin of cosmic rays. Cosmic ray, gamma ray, and neutrino observatories are reaching the necessary sensitivity to study the highest energy cosmic accelerators and to begin the use of cosmic particles to study particle interactions above laboratory energies. The number of known gamma-ray sources has increased by orders of magnitude. Possible cosmic ray sources have narrowed down with the confirmation of an ankle and the GZK-like spectral feature at the highest energies. Anisotropies in the distribution of arrival directions of cosmic rays at intermediate energies show a complex local neighborhood of the Galaxy. At the highest energies the dawn of particle astronomy is still challenging while composition related measurements point to a change in the composition or the interaction of cosmic rays at ultrahigh energies. A clear resolution of the ultrahigh energy mystery calls for a significant increase in statistics of cosmic ray and neutrino observations.

The influences of the Magellanic Clouds on the Galaxy: Pole shift, warp, and star formation history

astro-ph — Fri, 03 Feb 2012 01:51:22 +0000

We investigate how the Large Magellanic Cloud (LMC) influences the evolution of the Galaxy after the LMC enters into the virial radius of the dark matter halo of the Galaxy for the first time. Both the Galaxy and the LMC are modeled as N-body particles in our models so that the dynamical influences of the LMC on the Galaxy can be investigated in a fully self-consistent manner. Furthermore, the orbital parameters for the LMC are carefully chosen such that the present location of the LMC in the Galaxy can be rather precisely reproduced in our simulations. We particularly investigate the influences of the LMC on the precession rate, the outer stellar and gaseous structures, and the star formation history of the Galaxy. Our principals results are summarized as follows. The LMC-Galaxy dynamical interaction can cause “pole shift” (or irregular precession/nutation) of the Galaxy and the typical rate of pole shift (dot {\theta}_{d}) is ~2 degree Gyr^{-1} corresponding to ~ 7 muas yr^{-1}. The LMC-Galaxy interaction induces the formation of the outer warp structures of the Galaxy, which thus confirms the results of previous numerical simulations on the formation of the Galactic warp. The LMC-Galaxy interaction also induces the formation of outer (R>20 kpc) spiral arms and increases the vertical velocity dispersion of the outer disk significantly. The mean star formation rate of the Galaxy for the last several Gyrs can be hardly influenced by the LMC’s tidal force. The age and metallicity distribution of stars in the solar-neighborhood (7 kpc < R < 10 kpc) for the last several Gyr can be only slightly changed by the past LMC-Galaxy interaction. Based on these results, we discuss how the possible ongoing Galactic pole shift with 10 muas yr^{-1} can be detected by future observational studies by GAIA.

Radio Imaging of the NGC 2024 FIR 5/6 Region: a Hypercompact H II Region Candidate in Orion

astro-ph — Fri, 03 Feb 2012 01:51:10 +0000

The NGC 2024 FIR 5/6 region was observed in the 6.9 mm continuum with an angular resolution of about 1.5 arcsec. The 6.9 mm continuum map shows four compact sources, FIR 5w, 5e, 6c, and 6n, as well as an extended structure of the ionization front associated with the optical nebulosity. FIR 6c has a source size of about 0.4 arcsec or 150 AU. The spectral energy distribution (SED) of FIR 6c is peculiar: rising steeply around 6.9 mm and flat around 1 mm. The possibility of a hypercompact H II region is explored. If the millimeter flux of FIR 6c comes from hot ionized gas heated by a single object at the center, the central object may be a B1 star of about 5800 solar luminosities and about 13 solar masses. The 6.9 mm continuum of FIR 6n may be a mixture of free-free emission and dust continuum emission. Archival data show that both FIR 6n and 6c exhibit water maser activity, suggesting the existence of shocked gas around them. The 6.9 mm continuum emission from FIR 5w has a size of about 1.8 arcsec or 760 AU. The SEDs suggest that the 6.9 mm emission of FIR 5w and 5e comes from dust, and the masses of the dense molecular gas are about 0.6 and 0.5 solar masses, respectively.

Surface chemistry in the interstellar medium – I – H2 formation by Langmuir-Hinshelwood and Eley-Rideal mechanisms

astro-ph — Fri, 03 Feb 2012 01:50:54 +0000

H2 formation remains a major issue for the understanding of interstellar physics. We investigate H2 formation in the interstellar medium at the light of the most recent experimental and theoretical data. We implemented detailed H2 formation mechanisms on grains surface in the Meudon PDR code : i) Langmuir-Hinshelwood mechanism taking into account the contribution of the different sizes of dust grains in the diffusion processes and ii) the Eley-Rideal mechanism. We show that, thanks to these processes, H2 can be formed even in regions where dust temperature is larger than 25 K. We also show that formation by Eley-Rideal mechanism can be a significant source of heating of the gas. We derive line intensities for various astrophysical conditions. Such an approach results in an enhanced H2 formation rate compared to the standard formation determined by observations in absorption in the UV. We derive some H2 line intensities for isobaric and isochoric models.

Transformations between WISE and 2MASS, SDSS, BVI photometric systems: II. Transformation equations for red clump stars

astro-ph — Fri, 03 Feb 2012 01:50:40 +0000

We present colour transformations for the conversion of the Wide-Field Survey Explorer (WISE) W1, W2, and W3 magnitudes to the Johnson-Cousins (BVIc), Sloan Digital Sky Survey (gri), and Two Micron All Sky Survey JHKs photometric systems, for red clump (RC) stars. RC stars were selected from the Third Radial Velocity Experiment (RAVE) Data Release (DR3). The apparent magnitudes were collected by matching the coordinates of this sample with different photometric catalogues. The final sample (355 RC stars) used to obtain metallicity dependent-and free of metallicity- transformations between WISE and Johnson-Cousins, SDSS, 2MASS photometric systems. These transformations combined with known absolute magnitudes at shorter wavelengths can be used in space density determinations for the Galactic (thin and thick) discs at distances larger than the ones evaluated with JHKs photometry alone, hence providing a powerful tool in the analysis of Galactic structure.

Bayesian mixture models for Poisson astronomical images

astro-ph — Fri, 03 Feb 2012 01:50:25 +0000

Astronomical images in the Poisson regime are typically characterized by a spatially varying cosmic background, large variety of source morphologies and intensities, data incompleteness, steep gradients in the data, and few photon counts per pixel. The Background-Source separation technique is developed with the aim to detect faint and extended sources in astronomical images characterized by Poisson statistics. The technique employs Bayesian mixture models to reliably detect the background as well as the sources with their respective uncertainties. Background estimation and source detection is achieved in a single algorithm. A large variety of source morphologies is revealed. The technique is applied in the X-ray part of the electromagnetic spectrum on ROSAT and Chandra data sets and it is under a feasibility study for the forthcoming eROSITA mission.

Cores in Infra-Red Dark Clouds (IRDCs) seen in the Hi-GAL survey between l = 300{\deg} and l = 330{\deg}

astro-ph — Fri, 03 Feb 2012 01:50:12 +0000

We have used data taken as part of the Herschel infrared Galactic Plane survey (Hi-GAL) to study 3171 infrared-dark cloud (IRDC) candidates that were identified in the mid-infrared (8 {\mu}m) by Spitzer (we refer to these as ‘Spitzer-dark’ regions). They all lie in the range l=300 – 330 \circ and |b| 6 1 \circ. Of these, only 1205 were seen in emission in the far-infrared (250-500 {\mu}m) by Herschel (we call these ‘Herschel-bright’ clouds). It is predicted that a dense cloud will not only be seen in absorption in the mid-infrared, but will also be seen in emission in the far-infrared at the longest Herschel wavebands (250-500 {\mu}m). If a region is dark at all wavelengths throughout the mid-infrared and far-infrared, then it is most likely to be simply a region of lower background infrared emission (a ‘hole in the sky’). Hence, it appears that previous surveys, based on Spitzer and other mid-infrared data alone, may have over-estimated the total IRDC population by a factor of 2. This has implications for estimates of the star formation rate in IRDCs in the Galaxy.We studied the 1205 Herschel-bright IRDCs at 250 {\mu}m, and found that 972 of them had at least one clearly defined 250-{\mu}m peak, indicating that they contained one or more dense cores. Of these, 653 (67 per cent) contained an 8-{\mu}m point source somewhere within the cloud, 149 (15 per cent) contained a 24-{\mu}m point source but no 8-{\mu}m source, and 170 (18 per cent) contained no 24-{\mu}m or 8-{\mu}m point sources. We use these statistics to make inferences about the lifetimes of the various evolutionary stages of IRDCs.

Applying the Background-Source separation algorithm to Chandra Deep Field South data

astro-ph — Fri, 03 Feb 2012 01:50:00 +0000

A probabilistic two-component mixture model allows one to separate the diffuse background from the celestial sources within a one-step algorithm without data censoring. The background is modeled with a thin-plate spline combined with the satellite’s exposure time. Source probability maps are created in a multi-resolution analysis for revealing faint and extended sources. All detected sources are automatically parametrized to produce a list of source positions, fluxes and morphological parameters. The present analysis is applied to the Chandra Deep Field South 2 Ms public released data. Within its 1.884 ks of exposure time and its angular resolution (0.984 arcsec), the Chandra Deep Field South data are particularly suited for testing the Background-Source separation algorithm.

A possible ultra strong and broad Fe Ka emission line in Seyfert 2 galaxy IRAS 00521-7054

astro-ph — Fri, 03 Feb 2012 01:49:49 +0000

We present XMM-Newton spectra of the Seyfert 2 Galaxy IRAS 00521-7054. A strong feature at ~6 keV (observer’s frame) can be formally fitted with a strong (EW=1.3+-0.3 keV in the rest frame) and broad Fe Ka line, extending down to 3 keV. The underlying X-ray continuum could be fitted with an absorbed powerlaw (with Gamma = 1.8+-0.2 and N_H = 5.9 x 10^22 cm^-2) plus a soft component. If due to relativistically smeared reflection by an X-ray illuminated accretion disk, the spin of the supermassive black hole is constrained to be 0.97^+0.03_-0.13 (errors at 90% confidence level for one interesting parameter), and the accretion system is viewed at an inclination angle of 37+-4 degree. This would be the first type 2 AGN reported with strong red Fe Ka wing detected which demands a fast rotating SMBH. The unusually large EW would suggest that the light bending effect is strong in this source. Alternatively, the spectra could be fitted by a dual absorber model (though with a global chi^2 higher by ~ 6 for 283 d.o.f) with N_H1 = 7.0 x 10^22 cm^-2 covering 100% of the X-ray source, and N_H2 = 21.7 x 10^22 cm^-2 covering 71%, which does not require an extra broad Fe Ka line.

Herschel-ATLAS: towards a sample of ~1000 strongly-lensed galaxies

astro-ph — Fri, 03 Feb 2012 01:49:35 +0000

While the selection of strongly lensed galaxies with 500{\mu}m flux density S_500>100 mJy has proven to be rather straightforward (Negrello et al. 2010), for many applications it is important to analyze samples larger than the ones obtained when confining ourselves to such a bright limit. Moreover, only by probing to fainter flux densities is possible to exploit strong lensing to investigate the bulk of the high-z star-forming galaxy population. We describe HALOS (the Herschel-ATLAS Lensed Objects Selection), a method for efficiently selecting fainter candidate strongly lensed galaxies, reaching a surface density of ~1.5-2 deg^-2, i.e. a factor of about 4 to 6 higher than that at the 100 mJy flux limit. HALOS will allow the selection of up to ~1000 candidate strongly lensed galaxies (with amplifications \mu>2) over the full H-ATLAS survey area. Applying HALOS to the H-ATLAS Science Demonstration Phase field (~14.4 deg^2) we find 31 candidate strongly lensed galaxies, whose candidate lenses are identified in the VIKING near-infrared catalog. Using the available information on candidate sources and candidate lenses we tentatively estimate a ~72% purity of the sample. The redshift distribution of the candidate lensed sources is close to that reported for most previous surveys for lensed galaxies, while that of candidate lenses extends to substantially higher redshifts than found in the other surveys. The counts of candidate strongly lensed galaxies are also in good agreement with model predictions (Lapi et al. 2011). Even though a key ingredient of the method is the deep near-infrared VIKING photometry, we show that H-ATLAS data alone allow the selection of a similarly deep sample of candidate strongly lensed galaxies with an efficiency close to 50%; a slightly lower surface density (~1.45 deg^-2) can be reached with a ~70% efficiency.

Neutral interstellar helium parameters based on IBEX-Lo observations and test particle calculations

astro-ph — Fri, 03 Feb 2012 01:49:08 +0000

Neutral Interstellar Helium (NISHe) is almost unaffected at the heliospheric interface with the interstellar medium and freely enters the solar system. It provides some of the best information on the characteristics of the interstellar gas in the Local Interstellar Cloud. The Interstellar Boundary Explorer (IBEX) is the second mission to directly detect NISHe. We present a comparison between recent IBEX NISHe observations and simulations carried out using a well-tested quantitative simulation code. Simulation and observation results compare well for times when measured fluxes are dominated by NISHe (and contributions from other species are small). Differences between simulations and observations indicate a previously undetected secondary population of neutral helium, likely produced by interaction of interstellar helium with plasma in the outer heliosheath. Interstellar neutral parameters are statistically different from previous in situ results obtained mostly from the GAS/Ulysses experiment, but they do agree with the local interstellar flow vector obtained from studies of interstellar absorption: the newly-established flow direction is ecliptic longitude 79.2 deg, latitude -5.1 deg, the velocity is \sim 22.8 km/s, and the temperature is 6200 K. These new results imply a markedly lower absolute velocity of the gas and thus significantly lower dynamic pressure on the boundaries of the heliosphere and different orientation of the Hydrogen Deflection Plane compared to prior results from Ulysses. A different orientation of this plane also suggests a new geometry of the interstellar magnetic field and the lower dynamic pressure calls for a compensation by other components of the pressure balance, most likely a higher density of interstellar plasma and strength of interstellar magnetic field.

Tunable filter imaging of high redshift quasar fields

astro-ph — Fri, 03 Feb 2012 01:48:54 +0000

We have used the Taurus Tunable Filter to search for Lyman alpha emitters in the fields of three high redshift quasar fields: two at z~2.2 (MRC B1256-243 and MRC B2158-206) and one at z~4.5 (BR B0019-1522). Our observations had a field of view of around 35 square arcminutes, and reached AB magnitudes of magnitudes of ~21 (MRC B1256-243), ~22 (MRC B2158-206), and ~22.6 (BR B0019-1522), dependent on wavelength. We have identified candidate emission line galaxies in all three of the fields, with the higher redshift field being by far the richest. By combining our observations with simulations of the instrumental response, we estimate the total density of emission line galaxies in each field. Seventeen candidate emission line galaxies were found in within 1.5 Mpc of BR0019-1522, a number density of 4.9 +/- 1.2 x 10^-3 Mpc^-3, suggesting a significant galaxy overdensity at z~4.5.

Chemical complexity in NGC1068

astro-ph — Fri, 03 Feb 2012 01:48:41 +0000

We aimed to study the chemistry of the circumnuclear molecular gas of NGC1068, and to compare it with those of the starburst galaxies M82 and NGC253. Using the IRAM-30m telescope, we observed the inner 2 kpc of NGC1068 between 86.2 GHz and 115.6 GHz. We identified 35 spectral features, corresponding to 24 different molecular species. Among them, HC3N, SO, N2H+, CH3CN, NS, 13CN, and HN13C are detected for the first time in NGC1068. Assuming local thermodynamic equilibrium (LTE), we calculated the column densities of the detected molecules, as well as the upper limits to the column densities of some undetected species. The comparison among the chemistries of NGC1068, M82, and NGC253, suggests that, apart from X-rays, shocks also determine the chemistry of NGC1068. We propose the column density ratio between CH3CCH and HC3N as a prime indicator of the imprints of starburst and AGN environments in the circumnuclear interstellar medium. This ratio is, at least, 64 times larger in M82 than in NGC1068, and, at least, 4 times larger in NGC253 than in NGC1068. Finally, we used the UCL_CHEM and UCL_PDR chemical codes to constrain the origin of the species, as well as to test the influence of UV radiation fields and cosmic rays on the observed abundances.

Backreaction and the Covariant Formalism of General Relativity [Cross-Listing]

astro-ph — Fri, 03 Feb 2012 01:48:32 +0000

This thesis is a review of backreaction, which is a possible alternative to dark energy and modified gravity. We describe in detail the 3+1 covariant formalism and Frobenius’ theorem. We present the averaging procedure developed by Buchert, the Buchert equations and the generalization of these equations to the case of general matter. We then generalize to arbitrary number of spatial dimensions. We focus on the case of 2+1 dimensions, where the relation between the topology and the geometry of a surface imposes a global constraint on backreaction.

Possible optical counterpart of PSR J1357–6429

astro-ph — Fri, 03 Feb 2012 01:48:18 +0000

PSR J1357–6429 is a Vela-like radio pulsar that has been recently detected in X-rays and gamma-rays. It powers a compact tail-like X-ray pulsar wind nebula and X-ray-radio plerion associated with an extended TeV source HESS J1356–645. We have performed deep optical observations with the VLT to search for an optical counterpart of the pulsar and its nebula. A point-like source has been detected in V, R, and I bands whose centre position is within the 1-sigma error circle of the X-ray position of the pulsar, and whose colours are distinct from those of ordinary stars. We consider it as a candidate optical counterpart of the pulsar. If it is indeed the counterpart, its 5-sigma offset from the radio pulsar position, measured about 9 yr earlier, implies the transverse velocity of the pulsar in the range of 1600–2000 km s^{-1} at the distance of 2–2.5 kpc, making it the fastest moving pulsar known. The direction of the estimated proper motion coincides with the extension of the pulsar’s X-ray tail, suggesting that this is a jet. The tentative optical luminosity and efficiency of the pulsar are similar to those of the Vela pulsar, which also supports the optical identification. However, the candidate shows an unusually steep dereddened flux increase towards the infrared with a spectral index of about 5, not typical for optical pulsars. It implies a strong double-knee spectral break in the pulsar emission between the optical and X-rays. The reasons for the spectral steepness are unclear. It may be caused by a possible nebula knot projected to the jet and strongly overlapped with the pulsar, as is observed for the Crab, where the knot has the spectrum significantly steeper than that of the pulsar. We find no other signs of the pulsar nebula in the optical. Alternatively, the detected source can be a faint AGN, not seen yet in other spectral domains.

Optical Integral Field Spectroscopy of NGC 5850

astro-ph — Fri, 03 Feb 2012 01:48:05 +0000

Here we present the preliminary results of the analysis of VIMOS observations of the central 4.5 kpc of the double-barred galaxy NGC 5850. We use optical diagnostic diagrams to study the main ionization mecahnism across the field of view confirming the LINER nature in the continuum peak location. Also a star-forming (SF) region is found close to it (0.46 kpc), a second SF region is located east of the center (1.6 kpc). Further the data reveals a complex nuclear gas kinematics which is likely to be dominated by the secondary bar.

Galactic Sources Science With Agile: The Case Of The Carina Region

astro-ph — Fri, 03 Feb 2012 01:47:04 +0000

During its first 2 years of operation, the gamma-ray AGILE satellite accumulated an extensive dataset for the Galactic plane. The data have been monitored for transient sources and several gamma-ray sources were detected. Their variability and possible association were studied. In this talk we will focus on the results of extensive observations of the Carina Region during the time period 2007 July – 2009 January, for a total livetime of ~130 days. The region is extremely complex, hosting massive star formation, with the remarkable colliding wind binary Eta Carinae, massive star clusters and HII regions (e.g. NGC 3324, RCW49, Westerlund II) and a giant molecular cloud extending over 150 pc (between l=284.7 and l=289). The Carina Nebula itself is the largest and IR highest surface brightness nebula of the Southern emisphere. We monitored several gamma ray sources in the Carina Region. In particular we detect a gamma ray source (1AGL J1043-5931) consistent with the position of Eta Carinae and report a remarkable 2-days gamma-ray flaring episode from this source on 2008 Oct 11-13. If 1AGL J1043-5931 is associated with the Eta Car system, our data provides the long sought first detection above 100 MeV of a colliding wind binary.

A planetary system around the nearby M dwarf GJ 667C with at least one super-Earth in its habitable zone

astro-ph — Fri, 03 Feb 2012 01:46:45 +0000

We re-analyze 4 years of HARPS spectra of the nearby M1.5 dwarf GJ 667C available through the ESO public archive. The new radial velocity (RV) measurements were obtained using a new data analysis technique that derives the Doppler measurement and other instrumental effects using a least-squares approach. Combining these new 143 measurements with 41 additional RVs from the Magellan/PFS and Keck/HIRES spectrometers, reveals 3 additional signals beyond the previously reported 7.2-day candidate, with periods of 28 days, 75 days, and a secular trend consistent with the presence of a gas giant (Period sim 10 years). The 28-day signal implies a planet candidate with a minimum mass of 4.5 Mearth orbiting well within the canonical definition of the star’s liquid water habitable zone, this is, the region around the star at which an Earth-like planet could sustain liquid water on its surface. Still, the ultimate water supporting capability of this candidate depends on properties that are unknown such as its albedo, atmospheric composition and interior dynamics. The 75-day signal is less certain, being significantly affected by aliasing interactions among a potential 91-day signal, and the likely rotation period of the star at 105 days detected in two activity indices. GJ 667C is the common proper motion companion to the GJ 667AB binary, which is metal poor compared to the Sun. The presence of a super-Earth in the habitable zone of a metal poor M dwarf in a triple star system, supports the evidence that such worlds should be ubiquitous in the Galaxy.

Constraining the dark energy and smoothness parameter with SNe Ia and Gamma-Ray Bursts

astro-ph — Fri, 03 Feb 2012 01:45:56 +0000

The existence of inhomogeneities in the observed Universe modifies the distance-redshift relations thereby affecting the results of cosmological tests in comparison to the ones derived assuming spatially uniform models. By modeling the inhomogeneities through a generalized Zeldovich-Kantowski-Dyer-Roeder (ZKDR) approach which is phenomenologically characterized by a smoothness parameter $\alpha$, we rediscuss the constraints on the cosmic parameters based on Supernovae type Ia and Gamma-Ray Bursts (GRBs) data. The present analysis is restricted to a flat $\Lambda$CDM model with the reasonable assumption that $\Lambda$ does not clump. A $\chi^{2}$-analysis using 557 SNe Ia data from the Union2 Compilation Data (Amanullah {\it et al.} 2010) constrains the pair of parameters ($\Omega_m, \alpha$) to $\Omega_m=0.27_{-0.03}^{+0.08}$($2\sigma$) and $\alpha \geq 0.25$. A similar analysis based only on 59 Hymnium GRBs (Wei 2010) constrains the matter density parameter to be $\Omega_m= 0.35^{+0.62}_{-0.24}$ ($2\sigma$) while all values for the smoothness parameter are allowed. By performing a joint analysis, it is found that $\Omega_m = 0.27^{+0.06}_{-0.03}$ and $\alpha \geq 0.52$. As a general result, although considering that current GRB data alone cannot constrain the smoothness $\alpha$ parameter our analysis provides an interesting cosmological probe for dark energy even in the presence of inhomogeneities.

On the molecular gas content and SFR in Hickson Compact Groups: enhanced or deficient?

astro-ph — Fri, 03 Feb 2012 01:45:12 +0000

We study the effect of the extreme environment in Hickson Compact groups (HCGs) on the molecular gas mass, \mhtwo, and the star formation rate (SFR) of galaxies as a function of atomic hydrogen (HI) content and evolutionary phase of the group. We have selected a redshift limited (D$<$100 Mpc) sample of 88 galaxies in 20 HCGs with available atomic hydrogen (HI) VLA maps, covering a wide range of HI deficiencies and evolutionary phases of the groups, and containing at least one spiral galaxy. We derived the far-infrared (FIR) luminosity (\lfir) from IRAS data and used it as a tracer of the SFR. We calculated the HI mass, \lfir and \mhtwo deficiencies. The mean deficiencies of \lfir and \mhtwo of spiral galaxies in HCGs are close to 0, indicating that their average SFR and molecular gas content are similar to those of isolated galaxies. However, there are indications of an excess in \mhtwo\($\sim$ 50%) in spiral galaxies in HCGs which can be interpreted as either an enhanced molecular gas content or as a higher concentration of \mhtwo towards the center in comparison to galaxies in lower density environments. In contrast, the mean \mhi of spiral galaxies in HCGs is only 12% of the expected value. The specific star formation rate (sSFR= SFR/stellar mass) tends to be lower for galaxies with a higher \mhtwo\ or \mhi\ deficiency. This trend is not seen for the star formation efficiency (SFE=SFR/\mhtwo). We found tentative indications for an enhancement of \mhtwo\ in spiral galaxies in HCGs in an early evolutionary phase and a decrease in later phases. We suggest that this might be due to an enhancement of the conversion from atomic to molecular gas due to on-going tidal interactions in an early evolutionary phase, followed by HI stripping and a decrease of the molecular gas content because of lack of replenishment.

Double degenerate mergers as progenitors of high-field magnetic white dwarfs

astro-ph — Fri, 03 Feb 2012 01:44:58 +0000

High-field magnetic white dwarfs have been long suspected to be the result of stellar mergers. However, the nature of the coalescing stars and the precise mechanism that produces the magnetic field are still unknown. Here we show that the hot, convective, differentially rotating corona present in the outer layers of the remnant of the merger of two degenerate cores is able to produce magnetic fields of the required strength that do not decay for long timescales. We also show, using an state-of-the-art Monte Carlo simulator, that the expected number of high-field magnetic white dwarfs produced in this way is consistent with that found in the Solar neighborhood.

High Energy Neutrinos and Cosmic Rays

astro-ph — Fri, 03 Feb 2012 01:44:47 +0000

This is a summary of a series of lectures on the current experimental and theoretical status of our understanding of origin and nature of cosmic radiation. Specific focus is put on ultra-high energy cosmic radiation above ~10^17 eV, including secondary neutral particles and in particular neutrinos. The most important open questions are related to the mass composition and sky distributions of these particles as well as on the location and nature of their sources. High energy neutrinos at GeV energies and above from extra-terrestrial sources have not yet been detected and experimental upper limits start to put strong contraints on the sources and the acceleration mechanism of very high energy cosmic rays.

Nucleosynthesis and Gamma-Ray Line Spectroscopy with INTEGRAL

astro-ph — Fri, 03 Feb 2012 01:44:32 +0000

Cosmic nucleosynthesis co-produces unstable isotopes, which emit characteristic gamma-ray emission lines upon their radioactive decay that can be measured with SPI on INTEGRAL. High spectral resolution allows to derive velocity constraints on nucleosynthesis ejecta down to ~100 km/s. Core-collapse supernovae apparently do not always produce significant amounts of 44Ti, as in the Galaxy fewer sources than expected from the supernova rate have been found. INTEGRAL’s 44Ti data on the well-observed Cas A and SN1987A events are evidence that non-spherical explosions and 44Ti production may be correlated. Characteristic gamma-ray lines from radioactive decays of long-lived 26Al and 60Fe isotopes have been exploited to obtain information on the structure and dynamics of massive stars in their late evolution and supernovae, as their yields are sensitive to those details. The extended INTEGRAL mission establishes a database of sufficiently-deep observations of several specific regions of massive star groups, such as Cygnus, Carina, and Sco-Cen. In the inner Galaxy, 26Al nucleosynthesis gamma-rays help to unravel the Galaxy’s structure and the role of a central bar, as the kinematically-shifted 26Al gamma-ray line energy records the longitude-velocity behavior of hot interstellar gas. Thus, INTEGRAL has consolidated the feasibility of constraining cosmic nucleosynthesis through gamma-ray line observations. Due to its extended mission INTEGRAL maintains its chance to also see rare sufficiently-nearby events, such as a nova to provide first nova nucleosynthesis measurements of 7Be and 22Na production.

Dust effects on the derived Sersic indexes of disks and bulges in spiral galaxies

astro-ph — Fri, 03 Feb 2012 01:43:30 +0000

We present a theoretical study that quantifies the effect of dust on the derived Sersic indexes of disks and bulges. The changes in the derived parameters from their intrinsic values (as seen in the absence of dust) were obtained by fitting Sersic distributions on simulated images of disks and bulges produced using radiative transfer calculations and the model of Popescu et al. 2011. We found that dust has the effect of lowering the measured Sersic index in most cases, with stronger effects for disks and bulges seen through more optically thick lines of sight.

Period doubling and non-linear resonance in the black hole candidate IGR J17091-3624 ?

astro-ph — Fri, 03 Feb 2012 01:42:23 +0000

The two high frequency quasi periodic oscillations (HFQPOs) recently reported in the black hole candidate IGR J17091-3624 by Altamirano and Belloni (2012) are in a 5:2 frequency ratio (164 Hz to 66 Hz). This ratio is strongly suggestive of period doubling and nonlinear resonance analogous to phenomena known in RV Tauri-type pulsating stars (and recently discovered also in oscillations of RR Lyrae-type and of BL Herculis-type variables). An interpretation of the frequency ratio in terms of nonlinear interactions and a comparison with the HFQPOs reported in GRS 1915+105 may imply a mass of about 6 solar masses for the black hole in IGR J17091- 3624.

Local Interstellar Neutral Hydrogen sampled in-situ by IBEX

astro-ph — Fri, 03 Feb 2012 01:42:13 +0000

Hydrogen gas is the dominant component of the local interstellar medium. However, due to ionization and interaction with the heliosphere, direct sampling of neutral hydrogen in the inner heliosphere is more difficult than sampling the local interstellar neutral helium, which penetrates deep into the heliosphere. In this paper we report on the first detailed analysis of the direct sampling of neutral hydrogen from the local interstellar medium. We confirm that the arrival direction of hydrogen is offset from that of the local Helium component. We further report the discovery of a variation of the penetrating Hydrogen over the first two years of IBEX observations. Observations are consistent with hydrogen experiencing an effective ratio of outward solar radiation pressure to inward gravitational force greater than unity ({\mu}>1); the temporal change observed in the local interstellar hydrogen flux can be explained with solar variability.

The enigmatic black-hole candidate and X-ray transient IGR J17091-3624 in its quiescent state as seen with XMM-Newton

astro-ph — Fri, 03 Feb 2012 01:41:56 +0000

We report on two short XMM-Newton observations performed in August 2006 and February 2007 during the quiescence state of the enigmatic black hole candidate system IGR J17091-3624. During both observations the source was clearly detected. Although the errors on the estimated fluxes are large, the source appears to be brighter by several tens of percents during the February 2007 observation compared to the August 2006 observation. During both observations the 2-10 keV luminosity of the source was close to ~10^{33} erg/s for an assumed distance of 10 kpc. However, we note that the distance to this source is not well constrained and it has been suggested it might be as far as 35 kpc which would result in an order of magnitude higher luminosities. If the empirically found relation between the orbital period and the quiescence luminosity of black hole transients is also valid for IGR J17091-3624, then we can estimate an orbital period of >100 hours (>4 days) for a distance of 10 kpc but it could be as large as tens of days if the source is truly much further away. Such a large orbital period would be similar to GRS 1915+105 which has an orbital period of ~34 days. Orbital periods this large could possibly be connected to the fact that both sources exhibit the same very violent and extreme rapid X-ray variability which has so far not yet been seen from any other black hole system. Alternatively the orbital period of IGR J17091-3624 might be more in line with the other systems (<100 hours) but we happened to have observed the source in an episode of elevated accretion which was significantly higher than its true quiescent accretion rate. In that case, the absence or presence of extreme short-term variability properties as is seen for IGR J17091-3624 and GRS 1915+105 is not related to the orbital periods of these black hole systems.

Color Gradients in Galaxies Out to z~3: Dependence on Galaxy Properties

astro-ph — Fri, 03 Feb 2012 01:41:23 +0000

Using HST/ACS observations, we measure the color gradients of 3248 galaxies in the GOODS-South field out to z~3 and i_{AB}<25.5 and characterize their dependence on galaxy properties (luminosity, apparent magnitude, galaxy size, redshift and morphological type). The color gradient is measured by the difference of v-i color outside (R_{50}1, galaxies show increasingly bluer cores while the color of the outskirts does not change as rapidly. At z~2.5 and -22.0= 2 is concentrated in their central regions. These color gradients and their dependence on galaxy properties could also have a significant impact on shear measurements in upcoming weak lensing cosmological surveys.

A Comparison of the LVDP and {\Lambda}CDM Cosmological Models [Cross-Listing]

astro-ph — Fri, 03 Feb 2012 01:40:27 +0000

We compare the cosmological kinematics obtained via our law of linearly varying deceleration parameter (LVDP) with the kinematics obtained in the {\Lambda}CDM model. We show that the LVDP model is almost indistinguishable from the {\Lambda}CDM model up to the near future of our universe as far as the current observations are concerned, though their predictions differ tremendously into the far future.

The Nature of Extremely Red H-[4.5]>4 Galaxies revealed with SEDS and CANDELS

astro-ph — Fri, 03 Feb 2012 01:40:08 +0000

We have analysed a sample of 25 extremely red H-[4.5]>4 galaxies, selected using 4.5 micron data from the Spitzer SEDS survey and deep H-band data from the Hubble Space Telescope (HST) CANDELS survey, over ~180 square arcmin of the UKIDSS Ultra Deep Survey (UDS) field. Our aim is to investigate the nature of this rare population of mid-infrared (mid-IR) sources that display such extreme near-to-mid-IR colours. Using up to 17-band photometry (U through 8.0 microns), we have studied in detail their spectral energy distributions, including possible degeneracies in the photometric redshift/internal extinction (zphot-Av) plane. Our sample appears to include sources of very different nature. Between 45% and 75% of them are dust-obscured, massive galaxies at 3

The ionized gas in the CALIFA early-type galaxies I. Mapping two representative cases: NGC 6762 and NGC 5966

astro-ph — Fri, 03 Feb 2012 01:39:54 +0000

As part of the CALIFA survey, we conducted a thorough 2D analysis of the ionized gas in two E/S0 galaxies, NGC6762 and NGC5966, aiming to shed light on the nature of their warm ionized ISM. We present optical IFS obtained with the PMAS/PPAK spectrophotometer. To recover the nebular lines, we subtracted the underlying stellar continuum from the observed spectra using the STARLIGHT code. In NGC6762, the ionized gas and stellar emission display similar morphologies, while the emission line morphology is elongated in NGC5966, spanning ~6 kpc, and is oriented roughly orthogonal to the major axis of the stellar continuum ellipsoid. Whereas gas and stars are kinematically aligned in NGC6762, the gas is kinematically decoupled from the stars in NGC5966. A decoupled rotating disk or an ionization cone are two possible interpretations of the elongated ionized gas structure in NGC5966. The latter would be the first ionization cone of such a dimension detected within a weak emission-line galaxy. Both galaxies have weak emission-lines relative to the continuum [EW(Ha)< 3 A] and have low excitation, log([OIII]5007/Hb) < 0.5. Based on optical diagnostic ratios ([OIII]5007/Hb,[NII]6584/Ha,[SII]6717,6731/Ha,[OI]6300/Ha), both objects contain a LINER nucleus and an extended LINER-like gas emission. The emission line ratios do not vary significantly with radius or aperture, which indicates that the nebular properties are spatially homogeneous. The gas emission in NGC6762 can be best explained by photoionization by pAGB stars without the need of invoking any other excitation mechanism. In the case of NGC5966, the presence of a nuclear ionizing source seems to be required to shape the elongated gas emission feature in the ionization cone scenario, although ionization by pAGB stars cannot be ruled out.(abridged)

Discovery of Halpha satellite emission in a low state of the SW Sextantis star BB Doradus

astro-ph — Fri, 03 Feb 2012 01:39:40 +0000

BB Dor was observed during its low state state in 2009. Signatures of both binary components are revealed in the average optical spectrum; no signature of accretion is observed. Narrow emission lines of Halpha, HeI and Na-D, as well as TiO absorption troughs trace the motion of the irradiated secondary star. We detect two additional components in the Halpha emission line that share many characteristics of similar “satellite” lines observed in the low state of magnetic cataclysmic variables of AM Her type. It is the first time such emission components are detected for an SW Sex star.

Towards understanding the dynamics of the bar/bulge region in our Galaxy

astro-ph — Fri, 03 Feb 2012 01:39:11 +0000

I review some of the work on bars which is closely linked to the bar/bulge system in our Galaxy. Several independent studies, using totally independent methods, come to the same results about the 3D structure of a bar, i.e., that a bar is composed of a vertically thick inner part and a vertically thin outer part. I give examples of this from simulations and substantiate the discussion with input from orbital structure analysis and from observations. The thick part has a considerably shorter radial extent than the thin part. I then see how this applies to our Galaxy, where two bars have been reported, the COBE/DIRBE bar and the Long bar. Comparing their extents and making the reasonable and necessary assumption that our Galaxy has properties similar to those of other galaxies of similar type, leads to the conclusion that these two bars can not form a standard double bar system. I then discuss arguments in favour of the two bars being simply different parts of the same bar, the COBE/DIRBE bar being the thick inner part and the Long bar being the thin outer part of this bar. I also very briefly discuss some related new results. I first consider bar formation and evolution in disc galaxies with a gaseous component – including star formation, feedback and evolution – and a triaxial halo. Then I consider bar formation in a fully cosmological context using hydrodynamical LCDM simulations, where the host galaxies grow, accrete matter and significantly evolve during the formation and evolution of the bar.

CARMA follow-up of the northern unconfirmed PLANCK galaxy cluster candidates

astro-ph — Fri, 03 Feb 2012 01:38:47 +0000

We present CARMA observations of the three northern unconfirmed galaxy clusters discovered by the PLANCK satellite. We confirm the existence of two massive clusters (PLCKESZ G115.71+17.52 and PLCKESZ G121.11+57.01) at high significance. For these clusters, we present refined centroid locations from the 31 GHz CARMA data, as well as mass estimates obtained from a joint analysis of CARMA and PLANCK data. We do not detect the third candidate, PLCKESZ G189.84-37.24, and place an upper limit on its mass of M500 < 3.2 X 10^(14) M_SUN at 68% confidence. Considering our data and the characteristics of the PLANCK Early Release SZ Catalog, we conclude that this object is likely to be a cold-core object in the plane of our Galaxy. As a result, we estimate the purity of the ESZ Catalog to be greater than 99.5%.

Source Plane Reconstruction of The Bright Lensed Galaxy RCSGA 032727-132609

astro-ph — Fri, 03 Feb 2012 01:38:36 +0000

We present new HST/WFC3 imaging data of RCSGA 032727-132609, a bright lensed galaxy at z=1.7 that is magnified and stretched by the lensing cluster RCS2 032727-132623. Using this new high-resolution imaging, we modify our previous lens model (which was based on ground-based data) to fully understand the lensing geometry, and use it to reconstruct the lensed galaxy in the source plane. This giant arc represents a unique opportunity to peer into 100-pc scale structures in a high-redshift galaxy. This new source reconstruction will be crucial for a future analysis of the spatially-resolved rest-UV and rest-optical spectra of the brightest parts of the arc.

A third cluster of red supergiants in the vicinity of the massive cluster RSGC3

astro-ph — Fri, 03 Feb 2012 01:38:22 +0000

Recent studies have shown that the area around the massive, obscured cluster RSGC3 may harbour several clusters of red supergiants. In this paper, we analyse a clump of photometrically selected red supergiant candidates 20′ south of RSGC3 in order to confirm the existence of another of these clusters. Using medium-resolution infrared spectroscopy around 2.27 microns, we derived spectral types and velocities along the line of sight for the selected candidates, confirming their nature and possible association. We find a compact clump of eight red supergiants and four other candidates at some distance, all of them spectroscopically confirmed red supergiants. The majority of these objects must form an open cluster, which we name Alicante 10. Because of the high reddening and strong field contamination, the cluster sequence is not clearly seen in 2MASS or GPS-UKIDSS. From the observed sources, we derive E(J-Ks)=2.6 and d~6 kpc. Although the cluster is smaller than RSGC3, it has an initial mass in excess of 10000 solar masses, and it seems to be part of the RSGC3 complex. With the new members this association already has 35 spectroscopically confirmed red supergiants, confirming its place as one of the most active sites of recent stellar formation in the Galaxy.

A measurement of gravitational lensing of the microwave background using South Pole Telescope data

astro-ph — Fri, 03 Feb 2012 01:37:55 +0000

We use South Pole Telescope data from 2008 and 2009 to detect the non-Gaussian signature in the cosmic microwave background (CMB) produced by gravitational lensing and to measure the power spectrum of the projected gravitational potential. We constrain the ratio of the measured amplitude of the lensing signal to that expected in a fiducial LCDM cosmological model to be 0.86 +/- 0.16, with no lensing disfavored at 6.3 sigma. Marginalizing over LCDM cosmological models allowed by the WMAP7 results in a measurement of A_lens=0.90+/-0.19, indicating that the amplitude of matter fluctuations over the redshift range 0.5 <~ z <~ 5 probed by CMB lensing is in good agreement with predictions. We present the results of several consistency checks. These include a clear detection of the lensing signature in CMB maps filtered to have no overlap in Fourier space, as well as a "curl" diagnostic that is consistent with the signal expected for LCDM. We perform a detailed study of bias in the measurement due to noise, foregrounds, and other effects and determine that these contributions are relatively small compared to the statistical uncertainty in the measurement. We combine this lensing measurement with results from WMAP7 to improve constraints on cosmological parameters when compared to those from WMAP7 alone: we find a factor of 3.9 improvement in the measurement of the spatial curvature of the Universe, Omega_k=-0.0014+/-0.0172; a 10% improvement in the amplitude of matter fluctuations within LCDM, sigma_8=0.810+/ 0.026; and a 5% improvement in the dark energy equation of state, w=-1.04+/-0.40. When compared with the measurement of w provided by the combination of WMAP7 and external constraints on the Hubble parameter, the addition of the lensing data improve the measurement of w by 15% to give w=-1.087+/-0.096.

Can dust emission be used to map the interstellar medium in high-redshift galaxies? Results from the Herschel Reference Survey

astro-ph — Fri, 03 Feb 2012 01:37:42 +0000

It has often been suggested that an alternative to the standard CO/21-cm method for estimating the mass of the interstellar medium (ISM) in a galaxy might be to estimate the mass of the ISM from the continuum dust emission. In this paper, we investigate the potential of this technique using Herschel observations of ten galaxies in the Herschel Reference Survey and in the Herschel Virgo Cluster Survey. We show that the emission detected by Herschel is mostly from dust that has a temperature and emissivity index similar to that of dust in the local ISM in our galaxy, with the temperature generally increasing towards the centre of each galaxy. We calibrate the dust method using the CO and 21-cm observations to provide an independent estimate of the mass of hydrogen in each galaxy, solving the problem of the uncertain `X factor’ for the molecular gas by minimizing the dispersion in the ratio of the masses estimated using the two methods. With the calibration for the dust method and the estimate of the X-factor produced in this way, the dispersion in the ratio of the two gas masses is 30%, which gives an upper limit on the fundamental accuracy of the dust method. The calibration we obtain for the dust method is very similar to an independent Herschel measurement for M31 and to the calibration for the Milky Way from Planck measurements.

Limb darkening laws for two exoplanet host stars derived from 3D stellar model atmospheres

astro-ph — Fri, 03 Feb 2012 01:37:29 +0000

We compare limb darkening laws derived from 3D hydrodynamical model atmospheres and 1D hydrostatic MARCS models for the host stars of the two transiting exoplanet systems HD 209458 and HD 189733. The surface brightness distribution of the stellar disks is calculated using 3D LTE spectrum formation and opacity sampling. We test our predictions using least-squares fits of model light curves to primary eclipses that were observed with the Hubble Space Telescope (HST). The limb darkening law derived from the 3D model of HD 209458 between 2900 A and 5700 A produces significantly better fits to the HST data, removing systematic residuals that were previously observed for model light curves based on 1D predictions. This difference arises mainly from the shallower mean temperature structure of the 3D model, which is a consequence of the explicit simulation of surface granulation. In the case of HD 189733, the model atmospheres produce practically equivalent limb darkening curves between 2900 A and 5700 A, partly due to obstruction by spectral lines, and the data are not sufficient to distinguish between the light curves. We also analyze HST observations between 5350 A and 10500 A for this star; the 3D model leads to a better fit compared to 1D predictions. The significant improvement of fit quality for the HD 209458 system demonstrates the higher degree of realism of 3D models and the importance of surface granulation for the formation of the atmospheric radiation field of late-type stars. This result agrees well with recent investigations of limb darkening in the solar continuum and other observational tests. The case of HD 189733 is no contradiction as the model light curves are less sensitive to the temperature stratification of the atmosphere and the observed data in the 2900 A – 5700 A region are not sufficient to distinguish more clearly between 3D and 1D limb darkening.

Spectral Index and Non-Gaussianity in Supersymmetric Hybrid Inflation [Replacement]

astro-ph — Fri, 03 Feb 2012 01:37:10 +0000

We consider a supersymmetric hybrid inflation model with two inflaton fields. The superpotential during inflation is dominated by W=(\kappa S+\kappa’ S’)M^2, where S, S’ are inflatons carrying the same U(1)_R charge, \kappa, \kappa’ are dimensionless couplings, and M (\sim 10^{15-16} GeV) is a dimensionful parameter associated with a symmetry breaking scale. One light mass eigenstate drives inflation, while the other heavier mass eigenstate is stuck to the origin. The smallness of the lighter inflaton mass for the scalar spectral index n_s\approx 0.96, which is the center value of WMAP7, can be controlled by the ratio \kappa’/\kappa through the supergravity corrections. We also discuss the possibility of the two field inflation and large non-Gaussianity in this setup.

A Time-Asymmetric Process in Central Force Scatterings [Replacement]

astro-ph — Fri, 03 Feb 2012 01:36:58 +0000

We show that in attractive force fields a high speed particle with a small mass speeding through space, statistically loses energy by colliding softly and transversely with large masses that move slowly and randomly. Furthermore, we show that the opposite holds in repulsive force fields: the light particle statistically gains energy. We consider the large masses to be distant from one another such that a series of two-body scatterings would suffice for the statistical analysis. The difference of this process from equilibration is discussed.

Model for common growth of supermassive black holes, bulges and globular star clusters: ripping off Jeans clusters [Replacement]

astro-ph — Fri, 03 Feb 2012 01:36:05 +0000

It is assumed that a galaxy starts as a dark halo of a few million Jeans clusters (JCs), each of which consists of nearly a trillion micro brown dwarfs, MACHOs of Earth mass. JCs in the galaxy center heat up their MACHOs by tidal forces, which makes them expand, so that coagulation and star formation occurs. Being continuously fed by matter from bypassing JCs, the central star(s) may transform into a super massive black hole. It has a fast $t^3$ growth during the first mega years, and a slow $t^{1/3}$ growth at giga years. JCs disrupted by a close encounter with this black hole can provide matter for the bulge. Those that survive can be so agitated that they form stars inside them and become globular star clusters. Thus black holes mostly arise together with galactic bulges in their own environment and are about as old as the oldest globular clusters. The age 13.2 Gyr of the star HE 1523-0901 puts forward that the Galactic halo was sufficiently assembled at that moment. The star formation rate has a maximum at black hole mass $\sim4 \ 10^7M_\odot$ and bulge mass $\sim5\,10^{10}M_\odot$. In case of merging supermassive black holes the JCs passing near the galactic center provide ideal assistance to overcome the last parsec.

The size of the jet launching region in M87 [Replacement]

astro-ph — Fri, 03 Feb 2012 01:35:37 +0000

The supermassive black hole candidate at the center of M87 drives an ultra-relativistic jet visible on kiloparsec scales, and its large mass and relative proximity allow for event horizon scale imaging with very long baseline interferometry at millimeter wavelengths (mm-VLBI). Recently, relativistic magneto-hydrodynamic (MHD) simulations of black hole accretion flows have proven capable of launching magnetically-dominated jets. We construct time-dependent disc/jet models of the innermost portion of the M87 nucleus by performing relativistic radiative transfer calculations from one such simulation. We identify two types of models, jet-dominated or disc/jet, that can explain the spectral properties of M87, and use them to make predictions for current and future mm-VLBI observations. The Gaussian source size for the favored sky orientation and inclination from observations of the large-scale jet is 33-44 microarcseconds (~4-6 Schwarzschild radii) on current mm-VLBI telescopes, very similar to existing observations of Sgr A*. The black hole shadow, direct evidence of an event horizon, should be visible in future measurements using baselines between Hawaii and Mexico. Both models exhibit variability at millimeter wavelengths with factor of ~2 amplitudes on year timescales. For the low inclination of M87, the counter-jet dominates the event horizon scale millimeter wavelength emission from the jet-forming region.

Bayesian inference of galaxy formation from the K-band luminosity function of galaxies: tensions between theory and observation [Replacement]

astro-ph — Fri, 03 Feb 2012 01:35:23 +0000

We conduct Bayesian model inferences from the observed K-band luminosity function of galaxies in the local Universe, using the semi-analytic model (SAM) of galaxy formation introduced in Lu et al (2011). The prior distributions for the 14 free parameters include a large range of possible models. We find that some of the free parameters, e.g. the characteristic scales for quenching star formation in both high-mass and low-mass halos, are already tightly constrained by the single data set. The posterior distribution includes the model parameters adopted in other SAMs. By marginalising over the posterior distribution, we make predictions that include the full inferential uncertainties for the colour-magnitude relation, the Tully-Fisher relation, the conditional stellar mass function of galaxies in halos of different masses, the HI mass function, the redshift evolution of the stellar mass function of galaxies, and the global star formation history. Using posterior predictive checking with the available observational results, we find that the model family (i) predicts a Tully-Fisher relation that is curved; (ii) significantly over predicts the satellite fraction; (iii) vastly over predicts the HI mass function; (iv) predicts high-z stellar mass functions that have too many low mass galaxies and too few high mass ones. and (v) predicts a redshift evolution of the stellar mass density and the star formation history that are in moderate disagreement. These results suggest that some important processes are still missing in the current model family and we discuss a number of possible solutions to solve the discrepancies, such as interactions between galaxies and dark matter halos, tidal stripping, the bimodal accretion of gas, preheating, and a redshift-dependent initial mass function.

Vacuum polarization induced by a cosmic string in anti-de Sitter spacetime [Replacement]

astro-ph — Fri, 03 Feb 2012 01:34:58 +0000

In this paper we investigate the vacuum expectation values (VEVs) of the field squared and the energy-momentum tensor associated with a massive scalar quantum field induced by a generalized cosmic string in D-dimensional anti-de Sitter (AdS) spacetime. In order to develop this analysis we evaluate the corresponding Wightman function. As we shall observe, this function is expressed as the sum of two terms: the first one corresponds to the Wightman function in pure AdS bulk and the second one is induced by the presence of the string. The second contribution is finite at coincidence limit and is used to provide closed expressions for the parts in the VEVs of the field squared and the energy-momentum tensor induced by the presence of the string. Because the analysis of vacuum polarizations effects in pure AdS spacetime have been developed in the literature, here we are mainly interested in the investigation of string-induced effects. We show that the curvature of the background spacetime has an essential influence on the VEVs at distances larger than the curvature radius. In particular, at large distances the decay of the string-induced VEVs is power-law for both massless and massive fields. The string-induced parts vanish on the AdS boundary and they dominate the pure AdS part for points near the AdS horizon.

Probing Lorentz Violation in Neutrino Propagation from a Core-Collapse Supernova [Replacement]

astro-ph — Fri, 03 Feb 2012 01:34:43 +0000

Supernova explosions provide the most sensitive probes of neutrino propagation, such as the possibility that neutrino velocities might be affected by the foamy structure of space-time thought to be generated by quantum-gravitational (QG) effects. Recent two-dimensional simulations of the neutrino emissions from core-collapse supernovae suggest that they might exhibit variations in time on the scale of a few milliseconds. We analyze simulations of such neutrino emissions using a wavelet technique, and consider the limits that might be set on a linear or quadratic violation of Lorentz invariance in the group velocities of neutrinos of different energies, v/c = [1 \pm (E/M_{nuLV1})] or [1 \pm (E/M_{\nuLV2})^2], if variations on such short time scales were to be observed, where the mass scales M_{nuLVi} might appear in models of quantum gravity. We find prospective sensitivities to M_{nuLV1} ~ 2 X 10^{13} GeV and M_{nuLV2} ~ 10^6 GeV at the 95% confidence level, up to two orders of magnitude beyond estimates made using previous one-dimensional simulations of core-collapse supernovae. We also analyze the prospective sensitivities to scenarios in which the propagation times of neutrinos of fixed energies are subject to stochastic fluctuations.

Scaling Symmetry Makes Spherical Hydrostatics Integrable [Replacement]

astro-ph — Fri, 03 Feb 2012 01:34:15 +0000

Any symmetry reduces a second-order differential equation to a first integral: variational symmetries of the action (exemplified by central field dynamics) lead to conservation laws, but symmetries of only the equations of motion (exemplified by scale-invariant hydrostatics) yield first-order non-conservation laws between invariants. We obtain these non-conservation laws by extending Noether’s Theorem to non-variational symmetries and present a variational formulation of spherical adiabatic hydrostatics. For scale-invariant hydrostatics, we recover all the known properties of polytropes and define a core radius, inside which polytropes of index n share a common core mass density structure, and outside of which their envelopes differ. The Emden solutions (regular solutions of the Lane-Emden equation) are finally obtained, along with useful approximations. An appendix discusses the special n=3 polytrope in order to emphasize how the same mechanical structure allows different thermostatic structures in relativistic degenerate white dwarfs and zero age main sequence stars.

Thermonuclear fusion in dense stars: Electron screening, conductive cooling, and magnetic field effects [Replacement]

astro-ph — Fri, 03 Feb 2012 01:33:48 +0000

We study the plasma correlation effects on nonresonant thermonuclear reactions of carbon and oxygen in the interiors of white dwarfs and liquid envelopes of neutron stars. We examine the effects of electron screening on thermodynamic enhancement of thermonuclear reactions in dense plasmas beyond the linear mixing rule. Using these improved enhancement factors, we calculate carbon and oxygen ignition curves in white dwarfs and neutron stars. The energy balance and ignition conditions in neutron star envelopes are evaluated, taking their detailed thermal structure into account. The result is compared to the simplified “one-zone model,” which is routinely used in the literature. We also consider the effect of strong magnetic fields on the ignition curves in the ocean of magnetars.

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

astro-ph — Fri, 03 Feb 2012 01:33:36 +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.

Global Constraints on Effective Dark Matter Interactions: Relic Density, Direct Detection, Indirect Detection, and Collider [Replacement]

astro-ph — Fri, 03 Feb 2012 01:33:23 +0000

An effective interaction approach is used to describe the interactions between the spin 0 or spin 1/2 dark matter particle and the degrees of freedom of the standard model. We explore the effects of these effective interaction operators on (i) dark matter relic density, (ii) spin-independent and spin-dependent dark matter-nucleon scattering cross sections, (iii) cosmic antiproton and gamma ray fluxes from the galactic halo due to dark matter annihilation, and (iv) monojet and monophoton production plus missing energy at the Tevatron and the Large Hadron Collider (LHC). We combine the experimental data of relic density from WMAP7, spin-independent cross section from XENON100, spin-dependent cross section from XENON10, ZEPLIN-III, and SIMPLE, cosmic antiproton flux from PAMELA, cosmic gamma-ray flux from ${\it Fermi}$-LAT, and the monojet and monophoton data from the Tevatron and the LHC, to put the most comprehensive limits on each effective operator.

Picogauss magnetic fields in voids from ultra-high energy cosmic rays [Replacement]

astro-ph — Fri, 03 Feb 2012 01:32:35 +0000

We argue that ultra-high energy cosmic rays emitted by galaxy clusters result in electric currents in filaments of the large-scale structure that are sufficient to generate magnetic fields in voids of the magnitude of ~1e-12 G and the coherence length of up to tens of Mpc. These fields satisfy both the lower and upper observational bounds on magnetic fields in voids without a need of any primordial component.

Magnetic substructure in the northern Fermi Bubble revealed by polarized WMAP emission [Replacement]

astro-ph — Fri, 03 Feb 2012 01:32:23 +0000

We report a correspondence between giant, polarized microwave structures emerging north from the Galactic plane near the Galactic center and a number of GeV gamma-ray features, including the eastern edge of the recently-discovered northern Fermi Bubble. The polarized microwave features also correspond to structures seen in the all-sky 408 MHz total intensity data, including the Galactic center spur. The magnetic field structure revealed by the polarization data at 23 GHz suggests that neither the emission coincident with the Bubble edge nor the Galactic center spur are likely to be features of the local ISM. On the basis of the observed morphological correspondences, similar inferred spectra, and the similar energetics of all sources, we suggest a direct connection between the Galactic center spur and the northern Fermi Bubble.

The Curious Case of HU Aquarii – Dynamically Testing Proposed Planetary Systems [Replacement]

astro-ph — Fri, 03 Feb 2012 01:31:45 +0000

In early 2011, the discovery of two planets moving on surprisingly extreme orbits around the eclipsing polar cataclysmic variable system HU Aquraii was announced based on variations in the timing of mutual eclipses between the two central stars. We perform a detailed dynamical analysis of the stability of the exoplanet system as proposed in that work, revealing that it is simply dynamically unfeasible. We then apply the latest rigorous methods used by the Anglo-Australian Planet Search to analyse radial velocity data to re-examine the data used to make the initial claim. Using that data, we arrive at a significantly different orbital solution for the proposed planets, which we then show through dynamical analysis to be equally unfeasible. Finally, we discuss the need for caution in linking eclipse-timing data for cataclysmic variables to the presence of planets, and suggest a more likely explanation for the observed signal.

FM stars: A Fourier view of pulsating binary stars, a new technique for measuring radial velocities photometrically [Replacement]

astro-ph — Fri, 03 Feb 2012 01:31:31 +0000

Some pulsating stars are good clocks. When they are found in binary stars, the frequencies of their luminosity variations are modulated by the Doppler effect caused by orbital motion. For each pulsation frequency this manifests itself as a multiplet separated by the orbital frequency in the Fourier transform of the light curve of the star. We derive the theoretical relations to exploit data from the Fourier transform to derive all the parameters of a binary system traditionally extracted from spectroscopic radial velocities, including the mass function which is easily derived from the amplitude ratio of the first orbital sidelobes to the central frequency for each pulsation frequency. This is a new technique that yields radial velocities from the Doppler shift of a pulsation frequency, thus eliminates the need to obtain spectra. For binary stars with pulsating components, an orbital solution can be obtained from the light curve alone. We give a complete derivation of this and demonstrate it both with artificial data, and with a case of a hierarchical eclipsing binary with {\it Kepler} mission data, KIC 4150611 (HD 181469). We show that it is possible to detect Jupiter-mass planets orbiting $\delta$ Sct and other pulsating stars with our technique. We also show how to distinguish orbital frequency multiplets from potentially similar nonradial $m$-mode multiplets and from oblique pulsation multiplets.

Gaia Universe Model Snapshot : A statistical analysis of the expected contents of the Gaia catalogue [Replacement]

astro-ph — Fri, 03 Feb 2012 01:31:20 +0000

Context. This study has been developed in the framework of the computational simulations executed for the preparation of the ESA Gaia astrometric mission. Aims. We focus on describing the objects and characteristics that Gaia will potentially observe without taking into consideration instrumental effects (detection efficiency, observing errors). Methods. The theoretical Universe Model prepared for the Gaia simulation has been statistically analyzed at a given time. Ingredients of the model are described, giving most attention to the stellar content, the double and multiple stars, and variability. Results. In this simulation the errors have not been included yet. Hence we estimate the number of objects and their theoretical photometric, astrometric and spectroscopic characteristics in the case that they are perfectly detected. We show that Gaia will be able to potentially observe 1.1 billion of stars (single or part of multiple star systems) of which about 2% are variable stars, 3% have one or two exoplanets. At the extragalactic level, observations will be potentially composed by several millions of galaxies, half million to 1 million of quasars and about 50,000 supernovas that will occur during the 5 years of mission. The simulated catalogue will be made publicly available by the DPAC on the Gaia portal of the ESA web site http://www.rssd.esa.int/gaia/.

Harmonic in-painting of CMB sky by constrained Gaussian realization [Replacement]

astro-ph — Fri, 03 Feb 2012 01:31:05 +0000

The presence of astrophysical emissions between the last scattering surface and our vantage point requires us to apply a foreground mask on CMB sky map, leading to large cut around the Galactic equator and numerous holes. Since many CMB analyses, including non-Gaussianity study may be performed on a whole sky map in a more straightforward and reliable manner, it is of utmost importance to develop an efficient method to in-paint the CMB sky map, while still preserving statistical properties. In this letter, we consider Monte-Carlo simulation of constrained Gaussian field and derive it for CMB anisotropy in harmonic space, where a feasible implementation is possible with good approximation. We applied our method to the simulated data, which confirms the masked area is in-painted in a way compliant with the expected statistical properties. Subsequently, we applied our method to the WMAP foreground-reduced maps and investigated the anomalous alignment between quadrupole and octupole components. From our investigation, we find the alignment in the foreground-reduced maps is even higher than the ILC map. In particular, we find the highest alignment in the V band map, which has less foreground contamination than other bands. Therefore, we find it hard to attribute the alignment to residual foregrounds. Our method will be complementary to other efforts on in-painting or reconstructing the masked CMB data, and of great use to Planck surveyor and future missions.

The Relation Between Ejecta Velocity, Intrinsic Color, and Host-Galaxy Mass for High-Redshift Type Ia Supernovae

astro-ph — Thu, 02 Feb 2012 01:51:59 +0000

Recently, using a large low-redshift sample of Type Ia supernovae (SNe Ia), we discovered a relation between SN Ia ejecta velocity and intrinsic color that improves the distance precision of SNe Ia and reduces potential systematic biases related to dust reddening. No SN Ia cosmological results have yet made a correction for the “velocity-color” relation. To test the existence of such a relation and constrain its properties at high redshift, we examine a sample of 75 SNe Ia discovered and observed by the Sloan Digital Sky Survey-II (SDSS-II) Supernova Survey and Supernova Legacy Survey (SNLS). From each spectrum, we measure ejecta velocities at maximum brightness for the Ca H&K and Si II 6355 features, v_Ca^0 and v_Si^0, respectively. Using SN light-curve parameters, we determine the intrinsic B_max – V_max for each SN. Similar to what was found at low-redshift, we find that SNe Ia with higher ejecta velocity tend to be intrinsically redder than SNe Ia with lower ejecta velocity. The distributions of ejecta velocities for SNe Ia at low and high redshift are similar, indicating that current cosmological results should have little bias related to the velocity-color relation. Additionally, we find a slight (2.4-sigma significant) trend between SN Ia ejecta velocity and host-galaxy mass such that SNe Ia in high-mass host galaxies tend to have lower ejecta velocities as probed by v_Ca^0. These results emphasize the importance of spectroscopy for SN Ia cosmology.

Phase-space consistency of stellar dynamical models determined by separable augmented densities

astro-ph — Thu, 02 Feb 2012 01:51:42 +0000

Assuming the separable augmented density, it is always possible to construct a distribution function of a spherical population with any given density and anisotropy. We consider under what conditions the distribution constructed as such is in fact non-negative everywhere in the accessible phase-space. We first generalize known necessary conditions on the augmented density using fractional calculus. The condition on the radius part R(r^2) (whose logarithmic derivative is the anisotropy parameter) is equivalent to the complete monotonicity of R(1/w)/w. The condition on the potential part on the other hand is given by its derivative up to any order not greater than (3/2-beta) being non-negative where beta is the central anisotropy parameter. We also derive a specialized inversion formula for the distribution from the separable augmented density, which leads to sufficient conditions on separable augmented densities for the non-negativity of the distribution. The last generalizes the similar condition derived earlier for the generalized Cuddeford system to arbitrary separable systems.

Constraints on Neutrino Mass and Light Degrees of Freedom in Extended Cosmological Parameter Spaces

astro-ph — Thu, 02 Feb 2012 01:51:25 +0000

From a combination of probes including the cosmic microwave background (WMAP7+SPT), Hubble constant (HST), baryon acoustic oscillations (SDSS+2dFGRS), and supernova distances (Union2), we have explored the extent to which the constraints on the effective number of neutrinos and sum of neutrino masses are affected by our ignorance of other cosmological parameters, including the curvature of the universe, running of the spectral index, primordial helium abundance, evolving late-time dark energy, and early dark energy. In a combined analysis of the effective number of neutrinos and sum of neutrino masses, we find mild (2.2 sigma) evidence for additional light degrees of freedom. However, the effective number of neutrinos is consistent with the canonical expectation of 3 massive neutrinos and no extra relativistic species to within 1 sigma when allowing for evolving dark energy and relaxing the inflation prior on the curvature and running. The agreement improves with the possibility of an early dark energy component, itself constrained to be less than 5% of the critical density (95% CL) in our expanded parameter space. In extensions of the standard cosmological model, the derived amplitude of linear matter fluctuations sigma_8 is found to closely agree with low-redshift cluster abundance measurements. The sum of neutrino masses is robust to assumptions of the effective number of neutrinos, late-time dark energy, curvature, and running at the level of 1.2 eV (95% CL). The upper bound degrades to 2.0 eV (95% CL) when further including the early dark energy density and primordial helium abundance as additional free parameters. Even for the maximal extension of parameter space, Planck alone could determine the possible existence of extra relativistic species at 4 sigma confidence and constrain the sum of neutrino masses to 0.2 eV (68% CL).

Direct Detection of Dark Matter Debris Flows

astro-ph — Thu, 02 Feb 2012 01:51:00 +0000

Tidal stripping of dark matter from subhalos falling into the Milky Way produces narrow, cold tidal streams as well as more spatially extended “debris flows” in the form of shells, sheets, and plumes. Here we focus on the debris flow in the Via Lactea II simulation, and show that this incompletely phase-mixed material exhibits distinctive high-velocity behavior. Unlike tidal streams, which may not necessarily intersect the Earth’s location, debris flow is spatially uniform at 8 kpc and thus guaranteed to be present in the dark matter flux incident on direct detection experiments. At Earth-frame velocities greater than 450 km/s, debris flow comprises more than half of the dark matter at the Sun’s location, and up to 80% at even higher velocities. Therefore, debris flow is most important for experiments that are particularly sensitive to the high velocity tail of the dark matter distribution, such as searches for light or inelastic dark matter or experiments with directional sensitivity. We show that debris flow yields a distinctive recoil energy spectrum and a broadening of the distribution of incidence direction.

Gamma-Ray-Burst Host Galaxy Surveys at Redshift z>4: Probes of Star Formation Rate and Cosmic Reionization

astro-ph — Thu, 02 Feb 2012 01:50:40 +0000

Measuring the star formation rate (SFR) at high redshift is crucial for understanding cosmic reionization and formation of galaxies and black holes. Two common complementary approaches are Lyman-Break-Galaxy (LBG) surveys for large samples, and Gamma-Ray-Burst (GRB) observations for sensitivity to SFR in small galaxies. The z>4 GRB-inferred SFR is higher than the LBG rate, but the origin of the difference is difficult to understand, as both methods rely on several modeling assumptions. Using a physically motivated galaxy luminosity function model, with star formation in dark-matter halos with virial temperature T_vir>2e4 K (M_DM>2e8 M_sun), we show that GRB and LBG-derived SFRs are consistent if GRBs extend to faint galaxies (M_ABL_lim,z) of GRB hosts with L>L_lim. This fraction quantifies the missing star formation fraction in LBG surveys and constrains the mass-suppression scale for galaxy formation, with weak dependence on modeling assumptions. Because f_det(L>L_lim,z) corresponds to the ratio of star formation rates derived from LBG and GRB surveys, if these estimators are unbiased, measuring f_det(L>L_lim,z) also constrains the redshift evolution of the GRB production rate per unit mass of star formation, typically modeled as (1+z)^beta. Our analysis predicts significant success in detecting GRB hosts at z~5 with f_det(L>L_lim,z)~0.4, but rarer detections at z>6. A GRB-host survey reaching M_AB=-18 at z>4 (within reach of Hubble Space Telescope observations) will elucidate the nature and properties of star formation sites during the epoch of reionization.

Simplified Smooth Inflation with Observable Gravity Waves [Cross-Listing]

astro-ph — Thu, 02 Feb 2012 01:50:29 +0000

We consider a simplified version of supersymmetric smooth hybrid inflation which contains a single ultraviolet cutoff m_P = 2.4 x 10^{18} GeV, instead of the two cutoffs m_P and M_* ~ few x 10^{17} GeV that are normally employed. With global supersymmetry the scalar spectral index n_s ~ 0.97, which is in very good agreement with the WMAP observations. With a non-minimal Kahler potential, the supergravity version of the model is compatible with the current central values of n_s and also yields potentially observable gravity waves (tensor to scalar ratio r <~ 0.02).

The kinematic of HST-1 in the jet of M87

astro-ph — Thu, 02 Feb 2012 01:50:16 +0000

Aims: We aim to constrain the structural variations within the HST-1 region downstream of the radio jet of M87, in general as well as in connection to the episodes of activity at very high energy (VHE). Methods: We analyzed and compared 26 VLBI observations of the M87 jet, obtained between 2006 and 2011 with the Very Long Baseline Array (VLBA) at 1.7 GHz and the European VLBI Network (EVN) at 5 GHz. Results: HST-1 is detected at all epochs; we model-fitted its complex structure with two or more components, the two outermost of which display a significant proper motion with a superluminal velocity around ~4c. The motion of a third feature that is detected upstream is more difficult to characterize. The overall position angle of HST-1 has changed during the time of our observations from -65deg to -90deg, while the structure has moved by over 80 mas downstream. Our results on the component evolution suggest that structural changes at the upstream edge of HST-1 can be related to the VHE events.

Ohmic Heating Suspends, not Reverses, the Cooling Contraction of Hot Jupiters

astro-ph — Thu, 02 Feb 2012 01:49:57 +0000

We study the radius evolution of close-in extra-solar jupiters under Ohmic heating, a mechanism that was recently proposed to explain the large observed sizes of many of these planets. Planets are born with high entropy and they subsequently cool and contract. We focus on two cases: first, that ohmic heating commences when the planet is hot (high entropy); and second, that it commences after the planet has cooled. In the former case, we use analytical scalings and numerical experiments to confirm that Ohmic heating is capable of suspending the cooling as long as a few percent of the stellar irradiation is converted into Ohmic heating, and the planet has a surface wind that extends to pressures of ~10 bar or deeper. For these parameters, the radii at which cooling is stalled are consistent with (or larger than) the observed radii of most planets. The only two exceptions are WASP-17b and HAT-P-32b. In contrast to the high entropy case, we show that Ohmic heating cannot significantly re-inflate planets after they have already cooled. This leads us to suggest that the diversity of radii observed in hot jupiters may be partially explained by the different epochs at which they are migrated to their current locations.

High Spectral Resolution Measurement of the Sunyaev-Zel’dovich Effect Null with Z-Spec

astro-ph — Thu, 02 Feb 2012 01:49:41 +0000

The Sunyaev-Zel’dovich (SZ) effect spectrum crosses through a null where dT_CMB = 0 near nu_0 = 217 GHz. In a cluster of galaxies, nu_0 can be shifted from the canonical thermal SZ effect value by corrections to the SZ effect scattering due to the properties of the inter-cluster medium. We have measured the SZ effect in the hot galaxy cluster RX J1347.5-1145 with Z-Spec, an R ~ 300 grating spectrometer sensitive between 185 and 305 GHz. These data comprise a high spectral resolution measurement around the null of the SZ effect and clearly exhibit the transition from negative to positive dT_CMB over the Z-Spec band. The SZ null position is measured to be nu_0 = 225.8 \pm 2.5 (stat.) \pm 1.2 (sys.) GHz, which differs from the canonical null frequency by 3.0 sigma and is evidence for modifications to the canonical thermal SZ effect shape. Assuming the measured shift in nu_0 is due only to relativistic corrections to the SZ spectrum, we place the limit T_e = 17.1 \pm 5.3 keV from the zero-point measurement alone. By simulating the response of the instrument to the sky, we are able to generate likelihood functions in {y_0, T_e, v_pec} space. For v_pec = 0 km/s, we measure the best fitting SZ model to be y_0 = 4.6 (+0.6, -0.9) x 10^-4, T_e,0 = 15.2 (+12,-7.4) keV. When v_pec is allowed to vary, a most probable value of v_pec = +450 \pm 810 km/s is found.

The Cosmic History of Hot Gas Cooling and Radio AGN Activity in Massive Early-Type Galaxies

astro-ph — Thu, 02 Feb 2012 01:49:23 +0000

We study the X-ray properties of 393 optically selected early-type galaxies (ETGs) over the redshift range of z~0.0-1.2 in the Chandra Deep Fields. To measure the average X-ray properties of the ETG population, we use X-ray stacking analyses with a subset of 158 passive ETGs (148 of which were individually undetected in X-ray). This ETG subset was constructed to span the redshift ranges of z = 0.1-1.2 in the ~4 Ms CDF-S and ~2 Ms CDF-N and z = 0.1-0.6 in the ~250 ks E-CDF-S where the contribution from individually undetected AGNs is expected to be negligible in our stacking. We find that 55 of the ETGs are detected individually in the X-rays, and 12 of these galaxies have properties consistent with being passive hot-gas dominated systems (i.e., systems not dominated by an X-ray bright Active Galactic Nucleus; AGN). On the basis of our analyses, we find little evolution in the mean 0.5-2 keV to B-band luminosity ratio (L_X/L_B proportional to [1 + z]^1.2) since z~1.2, implying that some heating mechanism prevents the gas from cooling in these systems. We consider that feedback from radio-mode AGN activity could be responsible for heating the gas. We select radio AGNs in the ETG population using their far-infrared/radio flux ratio. Our radio observations allow us to constrain the duty cycle history of radio AGN activity in our ETG sample. We estimate that if scaling relations between radio and mechanical power hold out to z~1.2 for the ETG population being studied here, the average mechanical power from AGN activity is a factor of ~1.4-2.6 times larger than the average radiative cooling power from hot gas over the redshift range z~0-1.2. The excess of inferred AGN mechanical power from these ETGs is consistent with that found in the local Universe for similar types of galaxies.

CMB at 2×2 order: The dissipation of primordial acoustic waves and the observable part of the associated energy release

astro-ph — Thu, 02 Feb 2012 01:49:00 +0000

Silk damping of primordial small scale perturbations in the photon-baryon fluid due to diffusion of photons inevitably creates spectral distortions in the CMB. With the proposed CMB experiment PIXIE it might become possible to measure these distortions and thereby constrain the primordial power spectrum at comoving wavenumbers 50 Mpc^{-1} < k < 10^4 Mpc^{-1}. Since primordial fluctuations on these scales are completely erased by Silk damping, these distortions may provide the only way to shed light on otherwise unobservable aspects of inflationary physics. A consistent treatment of the primordial dissipation problem requires going to second order in perturbation theory, while thermalization of these distortions necessitates consideration of second order in Compton scattering energy transfer. Here we give a full 2×2 treatment for creation and evolution of spectral distortions due to the acoustic dissipation process, consistently including the effect of polarization and photon mixing in the free streaming regime. We show that 1/3 of the total energy (9/4 larger than previous estimate) stored in small scale temperature perturbations imprints observable spectral distortions, while the remaining 2/3 only raise the average CMB temperature, an effect that is unobservable. At high redshift dissipation is mainly mediated through the quadrupole anisotropies, while after recombination peculiar motions are most important. During recombination the damping of the higher multipoles is also significant. We compute the average distortion for several examples using CosmoTherm, analyzing their dependence on parameters of the primordial power spectrum. For one of the best fit WMAP7 cosmologies, with n_S=1.027 and n_run=-0.034, the cooling of baryonic matter practically compensates the heating from acoustic dissipation in the mu-era. (abridged)

Latest Observational Constraints to the Ghost Dark Energy Model by Using Markov Chain Monte Carlo Approach

astro-ph — Thu, 02 Feb 2012 01:48:33 +0000

Recently, the vacuum energy of the QCD ghost in a time-dependent background is proposed as a kind of dark energy candidate to explain the acceleration of the universe. In this model, the energy density of the dark energy is proportional to the Hubble parameter $H$, which is the Hawking temperature on the Hubble horizon of the Friedmann-Robertson-Walker (FRW) universe. In this paper, we perform a constraint on the ghost dark energy model with and without bulk viscosity, by using the Markov Chain Monte Carlo (MCMC) method and the combined latest observational data from the type Ia supernova compilations including Union2.1(580) and Union2(557), cosmic microwave background, baryon acoustic oscillation, and the observational Hubble parameter data.

Clumpy accretion onto black holes. I. Clumpy-ADAF structure and radiation

astro-ph — Thu, 02 Feb 2012 01:47:54 +0000

In this paper, we investigate the dynamics of clumps embedded in and confined by the advection-dominated accretion flows (ADAF), in which collisions among the clumps are neglected. We start from the collisionless Boltzmann equation and assume that interaction between the clumps and the ADAF is responsible for transporting angular momentum of clumps outward. The inner edge of the clumpy-ADAF is set to be the tidal radius of the clumps. We consider strong and weak coupling cases, in which the averaged properties of clumps follow the ADAF dynamics and mainly determined by the black hole potential, respectively. We get the analytical solution of the dynamics of clumps for the two cases. The velocity dispersion of clumps is one magnitude higher than the ADAF for the strong coupling case. For the weak coupling case, we find that the mean radial velocity of clumps is linearly proportional to the coefficient of the drag force. We show that the tidally disrupted clumps would lead to accumulation of the debris to form a debris disk in the Shakura-Sunyaev regime. The entire hot ADAF will be efficiently cooled down by photons from the debris disk, giving rise to collapse of the ADAF and quench the clumpy accretion. Subsequently, evaporation of the collapsed ADAF drives resuscitate of a new clumpy-ADAF, resulting in an oscillation of the global clumpy-ADAF. Applications of the present model are briefly discussed to X-ray binaries, ionization nuclear emission regions (LINERs) and BL Lac objects.

Star formation in self-gravitating disks in active galactic nuclei. II. Episodic formation of broad line regions

astro-ph — Thu, 02 Feb 2012 01:47:38 +0000

(abridged) We study the consequence of star formation (SF) in an self-gravity dominated accretion disk in quasars. The warm skins of the SF disk are governed by the radiation from the inner part of the accretion disk to form Compton atmosphere (CAS). The CAS are undergoing four phases to form broad line regions. Phase I is the duration of pure accumulation supplied by the SF disk. During phase II clouds begin to form due to line cooling and sink to the SF disk. Phase III is a period of preventing clouds from sinking to the SF disk through dynamic interaction between clouds and the CAS. Finally, phase IV is an inevitable collapse of the entire CAS through line cooling. This CAS evolution drives the episodic appearance of BLRs. Geometry and dynamics of BLRs can be self-consistently derived from the thermal instability of the CAS during phases II and III by linear analysis. The metallicity gradient of SF disk gives rise to different properties of clouds from outer to inner part of BLRs. We find that clouds have column density N_H 10^22 cm^{-2} in the metal-poor regions. The metal-rich clouds compose the high ionization line (HIL) regions whereas the metal-poor clouds are in low ionization line (LIL) regions. Metal-rich clouds in HIL regions will be blown away by radiation pressure, forming the observed outflows. The LIL regions are episodic due to the mass cycle of clouds with the CAS in response to continuous injection by the SF disk, giving rise to different types of AGNs. Based on SDSS quasar spectra, we identify a spectral sequence in light of emission line equivalent width from Phase I to IV. A key phase in the episodic appearance of the BLRs is bright type II AGNs with no or only weak BLRs. We discuss observational implications and tests of the theoretical predictions of this model.

Calculating energy storage due to topological changes in emerging active region NOAA AR 11112

astro-ph — Thu, 02 Feb 2012 01:47:21 +0000

The Minimum Current Corona (MCC) model provides a way to estimate stored coronal energy using the number of field lines connecting regions of positive and negative photospheric flux. This information is quantified by the net flux connecting pairs of opposing regions in a connectivity matrix. Changes in the coronal magnetic field, due to processes such as magnetic reconnection, manifest themselves as changes in the connectivity matrix. However, the connectivity matrix will also change when flux sources emerge or submerge through the photosphere, as often happens in active regions. We have developed an algorithm to estimate the changes in flux due to emergence and submergence of magnetic flux sources. These estimated changes must be accounted for in order to quantify storage and release of magnetic energy in the corona. To perform this calculation over extended periods of time, we must additionally have a consistently labeled connectivity matrix over the entire observational time span. We have therefore developed an automated tracking algorithm to generate a consistent connectivity matrix as the photospheric source regions evolve over time. We have applied this method to NOAA Active Region 11112, which underwent a GOES M2.9 class flare around 19:00 on Oct.16th, 2010, and calculated a lower bound on the free magnetic energy buildup of ~8.25 x 10^30 ergs over 3 days.

The GJ 436 System: Directly Determined Astrophysical Parameters of an M-Dwarf and Implications for the Transiting Hot Neptune

astro-ph — Thu, 02 Feb 2012 01:46:58 +0000

The late-type dwarf GJ 436 is known to host a transiting Neptune-mass planet in a 2.6-day orbit. We present results of our interferometric measurements to directly determine the stellar diameter ($R_{\star} = 0.455 \pm 0.018 R_{\odot}$) and effective temperature ($T_{\rm EFF} = 3416 \pm 54$ K). We combine our stellar parameters with literature time-series data, which allows us to calculate physical and orbital system parameters, including GJ 436’s stellar mass ($M_{\star} = 0.472^{+ 0.0636}_{- 0.0566} M_{\odot}$), planetary radius ($R_{p} = 0.370^{+ 0.0149}_{- 0.0145} R_{Jupiter}$), planetary mass ($M_{p} = 0.075^{+ 0.0076}_{- 0.0072} M_{Jupiter}$), implying a mean planetary density of $\rho_{p} = 1.48^{+ 0.116}_{- 0.103} \rho_{Jupiter}$. These values are generally in good agreement with previous literature estimates based on assumed stellar mass and photometric light curve fitting. Finally, we examine the expected phase curves of the hot Neptune GJ 436b, based on various assumptions concerning the efficiency of energy redistribution in the planetary atmosphere, and find that it could be constrained with {\it Spitzer} monitoring observations.

Panoramic Survey of Lyman \alpha\ Emitters at z=3.1

astro-ph — Thu, 02 Feb 2012 01:46:27 +0000

We present the results of the extensive narrow-band survey of Ly\alpha\ emission-line objects at z=3.1 in the 1.38 deg^2 area surrounding the high density region of star-forming galaxies at z=3.09 in the SSA22 field, as well as in the 1.04 deg^2 area of the three separated general blank fields. In total of 2161 Ly\alpha\ emitters, 1394 in the SSA22 fields and 767 in the general fields, respectively, are detected to the narrow-band AB magnitude limit of 25.73, which corresponds to the line flux of 1.8 x 10^{-17} erg s^{-1} cm^{-2} or luminosity of 1.5 x 10^{42} erg s^{-1} at z=3.1, above the observed equivalent width threshold, 190\AA . The average surface number density of the emitters at z=3.1 in the whole general fields above the thresholds is 0.20+-0.01 arcmin^{-2}. The SSA22 high-density region at z=3.09 whose peak local density is 6 times the average is found to be the most prominent outstanding structure in the whole surveyed area and is firmly identified as a robust `protocluster’ with the enough large sample. We also compared the overdensity of the 100 arcmin^2 and 700 arcmin^2 areas which contain the protocluster with the expected fluctuation of the dark matter as well as those of the model galaxies in cosmological simulations. We found that the peak height values of the overdensity correspond to be 8-10 times and 3-4 times of the expected standard deviations of the counts of Ly\alpha emitters at z=3.1 in the corresponding volume, respectively. We conclude that the structure at z=3.09 in the SSA22 field is a very significant and rare density peak up to the scale of 60 Mpc.

Primordial curvature perturbation during and at the end of multi-field inflation

astro-ph — Thu, 02 Feb 2012 01:46:10 +0000

We study the generation of the primordial curvature perturbation in multi-field inflation. Considering both the evolution of the perturbation during inflation and the effects generated at the end of inflation, we present a general formula for the curvature perturbation. We provide the analytic expressions of the power spectrum, spectral tilt and non-Gaussianity for the separable potentials of two inflaton scalars, and apply them to some specific models.

A 2% Distance to z=0.35 by Reconstructing Baryon Acoustic Oscillations – I : Methods and Application to the Sloan Digital Sky Survey

astro-ph — Thu, 02 Feb 2012 01:45:57 +0000

We apply the reconstruction technique to the clustering of galaxies from the SDSS DR7 LRG sample, sharpening the baryon acoustic oscillation (BAO) feature and achieving a 1.9% measurement of the distance to z=0.35. This is the first application of reconstruction of the BAO feature in a galaxy redshift survey. We update the reconstruction algorithm of Eisenstein et al, 2007 to account for the effects of survey geometry as well as redshift-space distortions and validate it on 160 LasDamas simulations. We demonstrate that reconstruction sharpens the BAO feature in the angle averaged galaxy correlation function, reducing the nonlinear smoothing scale \Sigma_nl from 8.1 Mpc/h to 4.4 Mpc/h. Reconstruction also significantly reduces the effects of redshift-space distortions at the BAO scale, isotropizing the correlation function. This sharpened BAO feature yields an unbiased distance estimate (< 0.2%) and reduces the scatter from 3.3% to 2.1%. We demonstrate the robustness of these results to the various reconstruction parameters, including the smoothing scale, the galaxy bias and the linear growth rate. Applying this reconstruction algorithm to the SDSS LRG DR7 sample improves the significance of the BAO feature in these data from 3.3 sigma for the unreconstructed correlation function, to 4.2 sigma after reconstruction. We estimate a relative distance scale D_V/r_s to z=0.35 of 8.88+/-0.17, where r_s is the sound horizon and D_V = (D_A^2/H)^{1/3} is a combination of the angular diameter distance D_A and Hubble parameter H. Assuming a sound horizon of 154.25 Mpc, this translates into a distance measurement D_V (z=0.35) = 1.356+/-0.025 Gpc. We find that reconstruction reduces the distance error in the DR7 sample from 3.5% to 1.9%, equivalent to a survey with three times the volume of SDSS.

A 2% Distance to z=0.35 by Reconstructing Baryon Acoustic Oscillations – II: Fitting Techniques

astro-ph — Thu, 02 Feb 2012 01:45:42 +0000

We present results from fitting the baryon acoustic oscillation (BAO) signal in the correlation function obtained from the first application of reconstruction to a galaxy redshift survey, namely, the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) luminous red galaxy (LRG) catalogue. We also introduce more careful approaches for deriving a suitable covariance matrix and fitting model for galaxy correlation functions. These all aid in obtaining a more accurate measurement of the acoustic scale and its error. We validate our reconstruction, covariance matrix and fitting techniques on 160 mock catalogues derived from the LasDamas simulations in real and redshift space. We then apply these techniques to the DR7 LRG sample and find that the error on the acoustic scale decreases from ~3.5% before reconstruction to ~1.9% after reconstruction. This factor of 1.8 reduction in the error is equivalent to the effect of tripling the survey volume. We also see an increase in our BAO detection confidence from ~3-sigma to ~4-sigma after reconstruction with our confidence level in measuring the correct acoustic scale increasing from ~3-sigma to ~5-sigma. Using the mean of the acoustic scale probability distributions produced from our fits, we find D_v/r_s = 8.89 +/- 0.31 before reconstruction and 8.88 +/- 0.17 after reconstruction.

A 2% Distance to z = 0.35 by Reconstructing Baryon Acoustic Oscillations – III : Cosmological Measurements and Interpretation

astro-ph — Thu, 02 Feb 2012 01:45:18 +0000

We use the 2% distance measurement from our reconstructed baryon acoustic oscillations (BAOs) signature using the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) Luminous Red Galaxies (LRGs) from Padmanabhan et al. (2012) and Xu et al. (2012) combined with cosmic microwave background (CMB) data from Wilkinson Microwave Anisotropy Probe (WMAP7) to measure parameters for various cosmological models. We find a 1.7% measurement of H_0 = 69.8 +/- 1.2 km/s/Mpc and a 5.0% measurement of \Omega_m = 0.280 +/- 0.014 for a flat Universe with a cosmological constant. These measurements of H_0 and Omega_m are robust against a range of underlying models for the expansion history. We measure the dark energy equation of state parameter w = -0.92 +/- 0.13, which is consistent with a cosmological constant. If curvature is allowed to vary, we find that the Universe is consistent with a flat geometry (\Omega_K = -0.004 +/- 0.005). We also use a combination of the 6 Degree Field Galaxy Survey BAO data, WiggleZ Dark Energy Survey data, Type Ia supernovae (SN) data, and a local measurement of the Hubble constant to explore cosmological models with more parameters. Finally, we explore the effect of varying the energy density of relativistic particles on the measurement of H_0.

Dithering Strategies and Point-Source Photometry

astro-ph — Thu, 02 Feb 2012 01:45:00 +0000

The accuracy in the photometry of a point source depends on the point-spread function (PSF), detector pixelization, and observing strategy. The PSF and pixel response describe the spatial blurring of the source, the pixel scale describes the spatial sampling of a single exposure, and the observing strategy determines the set of dithered exposures with pointing offsets from which the source flux is inferred. In a wide-field imaging survey, sources of interest are randomly distributed within the field of view and hence are centered randomly within a pixel. A given hardware configuration and observing strategy therefore have a distribution of photometric uncertainty for sources of fixed flux that fall in the field. In this article we explore the ensemble behavior of photometric and position accuracies for different PSFs, pixel scales, and dithering patterns. We find that the average uncertainty in the flux determination depends slightly on dither strategy, whereas the position determination can be strongly dependent on the dithering. For cases with pixels much larger than the PSF, the uncertainty distributions can be non-Gaussian, with rms values that are particularly sensitive to the dither strategy. We also find that for these configurations with large pixels, pointings dithered by a fractional pixel amount do not always give minimal average uncertainties; this is in contrast to image reconstruction for which fractional dithers are optimal. When fractional pixel dithering is favored, a pointing accuracy of better than $\sim 0.15$ pixel width is required to maintain half the advantage over random dithers.

FM stars: A Fourier view of pulsating binary stars, a new technique for measuring radial velocities photometrically

astro-ph — Thu, 02 Feb 2012 01:44:42 +0000

Observational Consequences of Dark Energy Decay

astro-ph — Thu, 02 Feb 2012 01:44:27 +0000

We consider the generic scenario of dark energy which arises through the latent heat of a hidden sector first order cosmological phase transition. This field could account for the extra radiation degree of freedom suggested by the CMB. We present the bubble nucleation solution for the viscous limit. The decay rate of the field is constrained by published KSZ data, and may be an explanation of current excess ISW correlations. Cross correlation of current and future surveys can further constrain or test the parameter space. The decay model is plausibly in the observable range, and avoids anthropic problems. This class of models is not well constrained by the popular dark energy figure of merit.

Trapped, Two-Armed, Nearly Vertical Oscillations in Disks with Toroidal Magnetic Fields II: Effects of Finite Thickness

astro-ph — Thu, 02 Feb 2012 01:44:09 +0000

We examine radial trapping of two-armed ($m=2$) vertical p-mode oscillations in geometrically thin relativistic disks which are vertically isothermal but terminated at a certain height by the presence of hot and low-density corona. The disks are assumed to be subject to toroidal magnetic fields. The oscillations are classified by $n$, a number related to the node number of oscillations in the vertical direction and starting from $n=1$. In modes with $n=1$, the frequencies of trapped oscillations depend little on the height of termination, but in modes with $n=2,3,…$ the frequencies decrease and the radial extends of trapped region become wide, as the termination height decreases. This study is a preparation to examine whether these oscillations can describe kilo-hertz quasi-periodic oscillations (kHz QPOs), horizontal branch oscillation (HBOs), and their correlations.

An Attempt to Describe Frequency Correlations among kHz QPOs and HBOs by Two-Armed Nearly Vertical Oscillations

astro-ph — Thu, 02 Feb 2012 01:43:52 +0000

We examine whether the two-armed ($m=2$) vertical p-mode oscillations trapped in the innermost region of magnetized accretion disks with finite disk thickness can describe kHz QPOs and HBOs in LMXBs. First, we derive the frequency-frequency correlation of the two basic oscillations (both are fundamental modes in the vertical direction, but one is the fundamental and the other the first overtone in the radial direction), and compare it with the observed frequency correlation of twin kHz QPOs. Results show that the calculated frequency correlation can well describe observed correlation with reasonable values of parameters. Second, we examine whether the observed frequency correlation between kHz QPOs and HBO can be described by regarding HBO as the first overtone oscillation in the vertical direction (and the fundamental in the radial direction). The results suggest that i) innermost parts of disks on the horizontal branch are strongly diminished in their vertical thickness (presumably by hot coronae) and ii) the branch is roughly a sequence of variations of magnetic fields or disk temperature.

S5 1803+78 revisited

astro-ph — Thu, 02 Feb 2012 01:43:36 +0000

We report on our optical monitoring of the BL Lac object S5 1803+78 from 1996 to 2011. The source showed no clear periodicity, but a time scale of about 1300 days between major flares is possibly present. No systematic trend of the color index with flux variations is evident, at variance with other BL Lacs. In one flare, however, the source was bluer in the rising phase and redder in the falling one. Two Gamma-ray flares were detected by Fermi-GST during our monitoring: on the occasion of only one of them we found simultaneous optical brightening. A one-zone Synchrotron Self Compton (SSC) model appears too simple to explain the source behavior.

Asiago eclipsing binaries program. IV. SZ Camelopardalis, a beta Cephei pulsator in a quadruple, eclipsing system

astro-ph — Thu, 02 Feb 2012 01:43:21 +0000

We present a spectroscopic and photometric analysis of the multiple system and early-type eclipsing binary SZ Cam (O9IV + B0.5V), which consists of an eclipsing SB2 pair of orbital period P=2.7 days in a long orbit (about 55 yrs) around a non-eclipsing SB1 pair of orbital period P=2.8 days. We have reconstructed the spectra of the individual components of SZ Cam from the observed composite spectra using the technique of spectral disentangling. We used them together with extensive and accurate BVI CCD photometry to obtain an orbital solution. Our photometry revealed the presence of a beta Cep variable in the SZ Cam hierarchical system, probably located within the non-eclipsing SB1 pair. The pulsation period is 0.33265+/-0.00005 days and the observed total amplitude in the B band is 0.0105 +/- 0.0005 mag. NLTE analysis of the disentangled spectra provided atmospheric parameters for all three components, consistent with those derived from orbital solution.

Gaia Universe Model Snapshot : A statistical analysis of the expected contents of the Gaia catalogue

astro-ph — Thu, 02 Feb 2012 01:43:00 +0000

High resolution imaging of the ATLBS regions: the radio source counts

astro-ph — Thu, 02 Feb 2012 01:42:40 +0000

The Australia Telescope Low-brightness survey (ATLBS; \cite{SESS10}) regions have been mosaic imaged at a radio frequency of 1.4 GHz with $6\arcsec$ angular resolution and 72 $\mu$Jy beam$^{-1}$ rms noise. The images cover 8.42 square degrees sky area and have no artifacts or imaging errors above the image thermal noise and, therefore, form a resource for attempting automated source identification and classification algorithms. Multi-resolution radio and optical r-band images were used to recognize multi-component sources and prepare a source list. Radio source counts in the flux density range 0.4-8.7 mJy are estimated, with corrections applied for noise bias, effective area correction and resolution bias. The resolution bias is mitigated to a great extent by using low resolution (beam FWHM $= 50\arcsec $) radio images, while effects of source confusion are removed by using high resolution images for identifying blended sources. The ATLBS counts are systematically lower than previous estimates. The work underscores the importance of using source lists—as opposed to component lists—and correcting for the noise bias in order to precisely estimate counts close to the image noise and determine the upturn at sub-mJy flux density.

Amorphous state in the mixed phase of quark-hadron phase transition in protoneutron stars

astro-ph — Thu, 02 Feb 2012 01:42:16 +0000

We study the quark-hadron mixed phase in protoneutron stars, where neutrinos are trapped and lepton number becomes a conserved quantity besides the baryon number and electric charge. Considering protoneutron star matter as a ternary system, the Gibbs conditions are applied together with the Coulomb interaction. We find there appears no crystalline (“pasta”) structure in the regime of high lepton-number fraction; the size of pasta becomes very large and the geometrical structure becomes mechanically unstable due to the charge screening effect. Consequently the whole system is separated into two bulk regions like an amorphous state, where the surface effect is safely neglected. The local charge neutrality is approximately attained there. After neutrinos are ejected, the matter becomes a binary system. Charge neutrality is globally ensured and the pasta structures appear there. These features are important to consider the quark-hadron phase transition during the evolution of protoneutron stars.

Period-Luminosity Relations for Cepheid Variables: From Mid-Infrared to Multi-Phase

astro-ph — Thu, 02 Feb 2012 01:41:59 +0000

This paper discusses two aspects of current research on the Cepheid period-luminosity (P-L) relation: the derivation of mid-infrared (MIR) P-L relations and the investigation of multi-phase P-L relations. The MIR P-L relations for Cepheids are important in the James Webb Space Telescope era for the distance scale issue, as the relations have potential to derive the Hubble constant within ~ 2% accuracy – a critical constraint in precision cosmology. Consequently, we have derived the MIR P-L relations for Cepheids in the Large and Small Magellanic Clouds, using archival data from Spitzer Space Telescope. We also compared currently empirical P-L relations for Cepheids in the Magellanic Clouds to the synthetic MIR P-L relations derived from pulsational models. For the study of multi-phase P-L relations, we present convincing evidence that the Cepheid P-L relations in the Magellanic Clouds are highly dynamic quantities that vary significantly when considered as a function of pulsational phase. We found that there is a difference in P-L relations as a function of phase between the Cepheids in each of the Clouds; the most likely cause for this is the metallicity difference between the two galaxies. We also investigated the dispersion of the multi-phase P-L relations, and found that the minimum dispersion do not differ significantly from the mean light P-L dispersion.

Radio-loud Magnetars as Detectors for Axions and Axion-like Particles [Cross-Listing]

astro-ph — Thu, 02 Feb 2012 01:41:26 +0000

We show that, by studying the arrival times of radio pulses from highly-magnetized transient beamed sources, it may be possible to detect light pseudo-scalar particles, such as axions and axion-like particles, whose existence could have considerable implications for the strong-CP problem of QCD as well as the dark matter problem in cosmology. Specifically, such light bosons may be detected with a much greater sensitivity, over a broad particle mass range, than is currently achievable by terrestrial experiments, and using indirect astrophysical considerations. The observable effect was discussed in Chelouche & Guendelman (2009), and is akin to the Stern-Gerlach experiment: the splitting of a photon beam naturally arises when finite coupling exists between the electro-magnetic field and the axion field. The splitting angle of the light beams linearly depends on the photon wavelength, the size of the magnetized region, and the magnetic field gradient in the transverse direction to the propagation direction of the photons. If radio emission in radio-loud magnetars is beamed and originates in regions with strong magnetic field gradients, then splitting of individual pulses may be detectable. We quantify the effect for a simplified model for magnetars, and search for radio beam splitting in the 2\,GHz radio light curves of the radio loud magnetar XTE\,J1810-197.

Consequences of spontaneous reconnection at a two-dimensional non-force-free current layer

astro-ph — Thu, 02 Feb 2012 01:41:11 +0000

Magnetic neutral points, where the magnitude of the magnetic field vanishes locally, are potential locations for energy conversion in the solar corona. The fact that the magnetic field is identically zero at these points suggests that for the study of current sheet formation and of any subsequent resistive dissipation phase, a finite beta plasma should be considered, rather than neglecting the plasma pressure as has often been the case in the past. The rapid dissipation of a finite current layer in non-force-free equilibrium is investigated numerically, after the sudden onset of an anomalous resistivity. The aim of this study is to determine how the energy is redistributed during the initial diffusion phase, and what is the nature of the outward transmission of information and energy. The resistivity rapidly diffuses the current at the null point. The presence of a plasma pressure allows the vast majority of the free energy to be transferred into internal energy. Most of the converted energy is used in direct heating of the surrounding plasma, and only about 3% is converted into kinetic energy, causing a perturbation in the magnetic field and the plasma which propagates away from the null at the local fast magnetoacoustic speed. The propagating pulses show a complex structure due to the highly non-uniform initial state. It is shown that this perturbation carries no net current as it propagates away from the null. The fact that, under the assumptions taken in this paper, most of the magnetic energy released in the reconnection converts internal energy of the plasma, may be highly important for the chromospheric and coronal heating problem.

Classical and quantum Big Brake cosmology for scalar field and tachyonic models [Cross-Listing]

astro-ph — Thu, 02 Feb 2012 01:40:53 +0000

We have studied a relation between the cosmological singularities in classical and quantum theory, comparing the classical and quantum dynamics in two models possessing the Big Brake singularity – the model based on a scalar field and one based on a tachyon field model. It was shown that in the tachyon model, the wave function of the universe is not obliged to vanish at the values of the variables, corresponding to the appearance of the classical Big Brake singularity. There is some kind of a classical – quantum correspondence, because as it was shown before, in the classical cosmological tachyon model exists an infinite one-parameter set of the cosmological evolutions, encountering and crossing the Big Brake singularity. In all the other cases – the Big Brake singularity in the scalar field model and the Big Bang and the Big Crunch singularities in both the tachyon and scalar field models we have observed the phenomenon of the quantum avoidance of singularities. It corresponds to the degeneration of the corresponding cosmological trajectories in classical theory.

Stability of de Sitter Solutions in Non-local Cosmological Models [Cross-Listing]

astro-ph — Thu, 02 Feb 2012 01:40:39 +0000

A non-local gravity model, which includes a function $f(\Box^{-1} R)$, where $\Box$ is the d’Alembert operator, is considered. For the model with an exponential $f(\Box^{-1} R)$ de Sitter solutions are explored, without any restrictions on the parameters. Using Hubble-normalized variables, the stability of the de Sitter solutions is investigated, with respect to perturbations in the Bianchi I metric, in the case of zero cosmological constant, and sufficient conditions for stability are obtained.

Estimations of the Distances of Stellar Collapses in the Galaxy by Analyzing the Energy Spectrum of Neutrino Bursts

astro-ph — Thu, 02 Feb 2012 01:40:23 +0000

The neutrino telescopes of the present generation, depending on their specific features, can reconstruct the neutrino spectra from a galactic burst. Since the optical counterpart could be not available, it is desirable to have at hand alternative methods to estimate the distance of the supernova explosion using only the neutrino data. In this work we present preliminary results on the method we are proposing to estimate the distance from a galactic supernova based only on the spectral shape of the neutrino burst and assumptions on the gravitational binding energy released an a typical supernova explosion due to stellar collapses.

Cluster Lenses

astro-ph — Thu, 02 Feb 2012 01:40:03 +0000

Clusters of galaxies are the most recently assembled, massive, bound structures in the Universe. As predicted by General Relativity, given their masses, clusters strongly deform space-time in their vicinity. Clusters act as some of the most powerful gravitational lenses in the Universe. Light rays traversing through clusters from distant sources are hence deflected, and the resulting images of these distant objects therefore appear distorted and magnified. Lensing by clusters occurs in two regimes, each with unique observational signatures. The strong lensing regime is characterized by effects readily seen by eye, namely, the production of giant arcs, multiple-images, and arclets. The weak lensing regime is characterized by small deformations in the shapes of background galaxies only detectable statistically. Cluster lenses have been exploited successfully to address several important current questions in cosmology: (i) the study of the lens(es) – understanding cluster mass distributions and issues pertaining to cluster formation and evolution, as well as constraining the nature of dark matter; (ii) the study of the lensed objects – probing the properties of the background lensed galaxy population — which is statistically at higher redshifts and of lower intrinsic luminosity thus enabling the probing of galaxy formation at the earliest times right up to the Dark Ages; and (iii) the study of the geometry of the Universe – as the strength of lensing depends on the ratios of angular diameter distances between the lens, source and observer, lens deflections are sensitive to the value of cosmological parameters and offer a powerful geometric tool to probe Dark Energy. In this review, we present the basics of cluster lensing and provide a current status report of the field.

Harmonic in-painting of CMB sky by constrained Gaussian realization

astro-ph — Thu, 02 Feb 2012 01:39:53 +0000

The chemical composition of CO-rich comet C/2009 P1 (Garradd) at Rh = 2.4 and 2.0 AU before perihelion

astro-ph — Thu, 02 Feb 2012 01:39:40 +0000

We quantified ten parent volatiles in comet C/2009 P1 (Garradd) before perihelion, through high-dispersion infrared spectra acquired with CRIRES at ESO’s VLT on UT 2011 August 07 (Rh = 2.4 AU) and September 17-21 (Rh = 2.0 AU). On August 07, water was searched but not detected at an upper limit (3{\sigma}) of 2.1 \times 10^28 s-1, while ethane was detected with a production rate of 6.1 \times 10^26 s-1 (apparent mixing ratio > 2.90%). On September 17-21, the mean production rate for water was 8.4 \times 10^28 s-1, and abundance ratios (relative to water) of detected trace species were: CO (12.51%), CH3OH (3.90%), CH4 (1.24%), C2H6 (1.01%) and HCN (0.36%). Upper limits (3{\sigma}) to abundances for four minor species were: NH3 (1.55%), C2H2 (0.13%), HDO (0.89%) and OCS (0.20%). Given the relatively large heliocentric distance, we explored the effect of water not being fully sublimated within our FOV and identified the ‘missing’ water fraction needed to reconcile the retrieved abundance ratios with the mean values found for “organics-normal”. The individual spatial profiles of parent volatiles and the continuum displayed rather asymmetric outgassing. Indications of H2O and CO gas being released in different directions suggest different active vents and/or the possible existence of polar and apolar ice aggregates in the nucleus. The high fractional abundance of CO identifies comet C/2009 P1 as a CO-rich comet.

Inversion of physical parameters in solar atmospheric seismology

astro-ph — Thu, 02 Feb 2012 01:39:21 +0000

Magnetohydrodynamic (MHD) wave activity is ubiquitous in the solar atmosphere. MHD seismology aims to determine difficult to measure physical parameters in solar atmospheric magnetic and plasma structures by a combination of observed and theoretical properties of MHD waves and oscillations. This technique, similar to seismology or helio-seismology, demands the solution of two problems. The direct problem involves the computation of wave properties of given theoretical models. The inverse problem implies the calculation of unknown physical parameters, by means of a comparison of observed and theoretical wave properties. Solar atmospheric seismology has been successfully applied to different structures such as coronal loops, prominence fine structures, spicules, or jets. However, it is still in its infancy. Far more is there to come. We present an overview of recent results, with particular emphasis in the inversion procedure.

Nonlinear Excitations in Strongly-Coupled Fermi-Dirac Plasmas

astro-ph — Thu, 02 Feb 2012 01:39:09 +0000

In this paper we use the conventional quantum hydrodynamics (QHD) model in combination with the Sagdeev pseudopotential method to explore the effects of Thomas-Fermi nonuniform electron distribution, Coulomb interactions, electron exchange and ion correlation on the large-amplitude nonlinear soliton dynamics in Fermi-Dirac plasmas. It is found that in the presence of strong interactions significant differences in nonlinear wave dynamics of Fermi-Dirac plasmas in the two distinct regimes of nonrelativistic and relativistic degeneracies exist. Furthermore, it is remarked that first-order corrections due to such interactions (which are proportional to the fine-structure constant) are significant on soliton dynamics in nonrelativistic plasma degeneracy regime rather than relativistic one. In the relativistic degeneracy regime, however, these effects become less important and the electron quantum-tunneling and Pauli-exclusion dominate the nonlinear wave dynamics. Hence, application of non-interacting Fermi-Dirac QHD model to study the nonlinear wave dynamics in quantum plasmas such as compact stars is most appropriate for the relativistic degeneracy regime.

HST/COS Observations of Thirteen New He II Quasars

astro-ph — Thu, 02 Feb 2012 01:38:54 +0000

The full reionization of intergalactic helium was a major event in the history of the IGM, and UV observations of the He II Gunn-Peterson trough allow us to characterize the end of this process at z~3. Due to intervening hydrogen absorption, quasars allowing such study are rare, with only 33 known in the literature, and most of those are very recent discoveries. We expand on our previous discovery work, and present 13 new He II quasars with redshifts 2.82 < z < 3.77, here selected with ~80% efficiency, and including several that are much brighter than the vast majority of those previously known. This is the largest sample of uniformly observed He II quasars covering such a broad redshift range, and they show evidence of IGM opacity increasing with redshift, as expected for the helium reionization epoch. No evidence of He II Ly{\alpha} quasar emission is seen in individual or averaged spectra, posing a problem for standard models of the broad line region. The current rapid advance in the study of He II quasars has been greatly facilitated by the Cosmic Origins Spectrograph on HST, and we discuss the instrumental and other subtleties that must be taken into account in IGM He II observations.

Birkhoff Theorem and Matter [Cross-Listing]

astro-ph — Thu, 02 Feb 2012 01:38:40 +0000

Birkhoff’s theorem for spherically symmetric vacuum spacetimes is a key theorem in studying local systems in general relativity theory. However realistic local systems are only approximately spherically symmetric and only approximately vacuum. In a previous paper, we showed the theorem remains approximately true in an approximately spherically symmetric vacuum space time. In this paper we prove the converse case: the theorem remains approximately true in a spherically symmetric, approximately vacuum space time.

Abrupt Change in Radiation-Width Distribution for 147Sm Neutron Resonances [Cross-Listing]

astro-ph — Thu, 02 Feb 2012 01:38:27 +0000

We obtained total radiation widths of s-wave resonances through R-matrix analysis of 147Sm(n,gamma) cross-sections. Distributions of these widths differ markedly for resonances below and above 300 eV, in stark contrast to long-established theory. We show that this change, as well as a similar change in the neutron-width distribution reported previously, are reflected in abrupt increases in both the average 147Sm(n,gamma) cross section and fluctuations about the average near 300 eV. Such effects could have important consequences for applications such as nuclear astrophysics and nuclear criticality safety.

A Census of High-Energy Observations of Galactic Supernova Remnants

astro-ph — Thu, 02 Feb 2012 01:38:16 +0000

We present the first public database of high-energy observations of all known Galactic supernova remnants (SNRs). In section 1 we introduce the rationale for this work motivated primarily by studying particle acceleration in SNRs, and which aims at bridging the already existing census of Galactic SNRs (primarily made at radio wavelengths) with the ever-growing but diverse observations of these objects at high-energies (in the X-ray and gamma-ray regimes). In section 2 we show how users can browse the database using a dedicated web front-end (http://www.physics.umanitoba.ca/snr/SNRcat). In section 3 we give some basic statistics about the records we have collected so far, which provides a summary of our current view of Galactic SNRs. Finally, in section 4, we discuss some possible extensions of this work. We believe that this catalogue will be useful to both observers and theorists, and timely with the synergy in radio/high-energy SNR studies as well as the upcoming new high-energy missions. A feedback form provided on the website will allow users to provide comments or input, thus helping us keep the database up-to-date with the latest observations.

Prospective Constraints on Neutrino Masses from a Core-Collapse Supernova [Cross-Listing]

astro-ph — Thu, 02 Feb 2012 01:38:05 +0000

We discuss the prospects for improved upper limits on neutrino masses that may be provided by a core-collapse supernova explosion in our galaxy, if it exhibits time variations in the neutrino emissions on the scale of a few milliseconds as suggested by recent two-dimensional simulations. Analyzing simulations of such neutrino emissions using the wavelet technique adopted in [1], we find that an upper limit m_nu ~ 0.14 eV could be established at the 95% confidence level if the time variations in emissions were to be preserved during neutrino propagation to the Earth.

High-energy emission from galaxies: the star-formation/gamma-ray connection

astro-ph — Thu, 02 Feb 2012 01:37:48 +0000

The impact of non-thermal processes on the spectral energy distributions of galaxies can be dramatic, but such processes are often neglected in considerations of their structure and evolution. Particle acceleration associated with high mass star formation and AGN activity not only leads to very broad band (radio-\gamma-ray) emission, but may also produce very significant feedback effects on galaxies and their environment. The recent detections of starburst galaxies at GeV and TeV energies suggest that \gamma-ray instruments have now reached the critical level of sensitivity to probe the connection between particle acceleration and star-formation in galaxies. In this paper we will try to summarise this recent progress, put it into a multi-wavelength context and also discuss the prospects for more precise and sensitive \gamma-ray measurements with the upcoming CTA observatory.

2M1155-79 (= T Cha B): A Low-mass, Wide-separation Companion to the Nearby, "Old" T Tauri Star T Cha

astro-ph — Thu, 02 Feb 2012 01:37:24 +0000

The early-K star T Cha, a member of the relatively nearby (D ~ 100 pc) epsilon Cha Association, is a relatively “old” (age ~7 Myr) T Tauri star that is still sporadically accreting from an orbiting disk whose inner regions are evidently now being cleared by a close, substellar companion. We report the identification, via analysis of proper motions, serendipitous X-ray imaging spectroscopy, and followup optical spectroscopy, of a new member of the epsilon Cha Association that is very likely a low-mass companion to T Cha at a projected separation of ~38 kAU. The combined X-ray and optical spectroscopy data indicate that the companion, T Cha B (= 2M1155-79), is a weak-lined T Tauri star (wTTS) of spectral type M3 and age ~<10 Myr. The serendipitous X-ray (XMM-Newton) observation of T Cha B, which targeted T Cha, also yields serendipitous detections of two background wTTS in the Chamaeleon cloud complex, including one newly discovered, low-mass member of the Cha cloud pre-MS population. T Cha becomes the third prominent example of a nearby, "old" yet still actively accreting, K-type pre-MS star/disk system (the others being TW Hya and V4046 Sgr) to feature a low-mass companion at very large (12-40 kAU) separation, suggesting that such wide-separation companions may affect the conditions and timescales for planet formation around solar-mass stars.

The McDonald Observatory Planet Search: New Long-Period Giant Planets, and Two Interacting Jupiters in the HD 155358 System

astro-ph — Thu, 02 Feb 2012 01:37:08 +0000

We present high-precision radial velocity (RV) observations of four solar-type (F7-G5) stars – HD 79498, HD 155358, HD 197037, and HD 220773 – taken as part of the McDonald Observatory Planet Search Program. For each of these stars, we see evidence of Keplerian motion caused by the presence of one or more gas giant planets in long-period orbits. We derive orbital parameters for each system, and note the properties (composition, activity, etc.) of the host stars. While we have previously announced the two-gas-giant HD 155358 system, we now report a shorter period for planet c. This new period is consistent with the planets being trapped in mutual 2:1 mean-motion resonance. We therefore perform an in-depth stability analysis, placing additional constraints on the orbital parameters of the planets. These results demonstrate the excellent long-term RV stability of the spectrometers on both the Harlan J. Smith 2.7 m telescope and the Hobby-Eberly telescope.

Improved visual detection of moving objects in astronomical images using color intensity projections with hue cycling

astro-ph — Thu, 02 Feb 2012 01:36:57 +0000

While fully automated methods for detecting faint moving objects in astronomical images – such as Kuiper belt objects (KBOs) – are constantly improving, visual detection still has a role to play especially when the fixed background is cluttered with stars. Color intensity projections (CIPs) using hue cycling – which combines a sequence of greyscale images into a single color image – aids in the visual detection of moving objects by highlighting them using color in an intuitive way. To demonstrate the usefulness of CIPs in detecting faint moving objects a sequence of 16 images from the SuprimeCam camera of the Subaru telescope were combined into a CIPs image. As well has making even faint moving objects easier to visually detect against a cluttered background, CCD artefacts were also more easily recognisable. The new Hyper SuprimeCam for the Subaru telescope – which will allow many short exposure images to be acquired with little dead time between images – should provide ideal data for use with the CIPs algorithm. In addition, the current search for KBOs to be targeted by the New Horizon’s spacecraft after its flyby of Pluto provides an excellent test case for the state of the art in faint moving object detection against a cluttered background.

Detection of chaos in RR Lyrae models

astro-ph — Thu, 02 Feb 2012 01:36:17 +0000

The period doubling phenomenon was recently discovered in RR Lyrae stars with the Kepler space telescope and has been theoretically explained by hydrodynamic calculations. However, peculiar solutions of the Florida-Budapest turbulent convective hydrodynamic code suggest that bifurcation cascade may evolve to chaos in these dynamical systems. We show that chaotic behaviour may be recovered from the radius variations of the model using the global flow reconstruction method. The fractal (Lyapunov) dimension of the underlying dynamical attractor is calculated to be ~2.2. Compared to the radius, the luminosity variations proved to be less suitable for such investigations due to their complexity. That suggest that even the continuous Kepler data would require transformation before conducting a similar analysis.

Kinematics & Chemistry of Halo Substructures: The Vicinity of the Virgo Over-Density

astro-ph — Thu, 02 Feb 2012 01:35:59 +0000

We present observations obtained with the AAT’s 2dF wide field spectrograph AAOmega of K-type stars located within a region of the sky which contains the Virgo Over-Density and the leading arm of the Sagittarius Stream. On the basis of the resulting velocity histogram we isolate halo substructures in these overlapping regions including Sagittarius and previously discovered Virgo groups. Through comparisons with N-body models of the Galaxy-Sagittarius interaction, we find a tri-axial dark matter halo is favoured and we exclude a prolate shape. This result is contradictory with other observations along the Sagittarius leading arm, which typically favour prolate models. We have also uncovered K-giant members of Sagittarius that are notably more metal poor ([Fe/H] = -1.7 +/- 0.3 dex) than previous studies. This suggests a significantly wider metallicity distribution exists in the Sagittarius Stream than formerly considered. We also present data on five carbon stars which were discovered in our sample.

The effect of asymmetric beams in the Wilkinson Microwave Anisotropy Probe experiment [Replacement]

astro-ph — Thu, 02 Feb 2012 01:35:46 +0000

We generate simulations of the CMB temperature field as observed by the WMAP satellite, taking into account the detailed shape of the asymmetric beams and scanning strategy of the experiment, and use these to re-estimate the WMAP beam transfer functions. This method avoids the need of artificially symmetrizing the beams, as done in the baseline WMAP approach, and instead measures the total convolution effect by direct simulation. We find only small differences with respect to the nominal transfer functions, typically less than 1% everywhere, and less than 0.5% at l<400. The net effect on the CMB power spectrum is less than 0.6%. The effect on all considered cosmological parameters are negligible. For instance, we find that the spectral index of scalar perturbations after taking into account the beam asymmetries is n_s = 0.964 +- 0.014, corresponding to a negative shift of -0.1 sigma compared to the previously released WMAP results. Our CMB sky simulations are made publicly available, and can be used for general studies of asymmetric beam effects in the WMAP data.

Recombination Lines of CII in the Spectra of Planetary Nebulae [Replacement]

astro-ph — Thu, 02 Feb 2012 01:35:35 +0000

The current report presents the work to investigate the recombination lines of CII in the spectra of planetary nebulae. Two CIII targets were prepared and used to generate theoretical data required in the investigation of recombination lines that arise from collisions between electrons and ions in thin plasma found in planetary nebulae and other astrophysical objects. One of these targets contains 9 atomic terms while the other contains 26 terms. For each one of these targets, theoretical data concerning bound and autoionizing states were generated in the intermediate coupling approximation by R-matrix and Autostructure codes and compared to experimental data. The comparison revealed very good agreement. These theoretical data were then used to generate emissivity data and compare it to the carbon recombination lines found in the observational line list of Zhang et al [2005] on the planetary nebula NGC 7027. The main tool used in this analysis is the `Emissivity’ code which is a program developed by the author [2010] in the course of this investigation to calculate the emissivity of transition lines from resonances and subsequent cascade decay. The results of the analysis from both targets using a least-squares optimization technique indicate a temperature of 10200-10500K of the line-emitting region.

The Role of Collective Neutrino Flavor Oscillations in Core-Collapse Supernova Shock Revival [Replacement]

astro-ph — Thu, 02 Feb 2012 01:35:26 +0000

We explore the effects of collective neutrino flavor oscillations due to neutrino-neutrino interactions on the neutrino heating behind a stalled core-collapse supernova shock. We carry out axisymmetric (2D) radiation-hydrodynamic core-collapse supernova simulations, tracking the first 400 ms of the post-core-bounce evolution in 11.2 solar mass and 15 solar mass progenitor stars. Using inputs from these 2D simulations, we perform neutrino flavor oscillation calculations in multi-energy single-angle and multi-angle single-energy approximations. Our results show that flavor conversions do not set in until close to or outside the stalled shock, enhancing heating by not more than a few percent in the most optimistic case. Consequently, we conclude that the postbounce pre-explosion dynamics of standard core-collapse supernovae remains unaffected by neutrino oscillations. Multi-angle effects in regions of high electron density can further inhibit collective oscillations, strengthening our conclusion.

Stochasticity, a variable stellar upper-mass limit, binaries and star-formation rate indicators [Replacement]

astro-ph — Thu, 02 Feb 2012 01:35:10 +0000

Using our Binary Population And Spectral Synthesis (BPASS) code we explore the effects on star-formation rate indicators of stochastically sampling the stellar initial mass function, adding a cluster mass dependent stellar upper-mass limit and including binary stars. We create synthetic spectra of young clusters and star-forming galaxies and compare these to observations of H(alpha) emission from isolated clusters and the relation between H(alpha) and FUV emission from nearby galaxies. We find that observations of clusters tend to favour a purely stochastic sampling of the initial mass function for clusters less than 100M(Sun), rather than the maximum stellar mass being dependant on the total cluster mass. It is more difficult to determine whether the same is true for more massive clusters. We also find that binary stars blur some of the observational differences that occur when a cluster-mass dependent stellar upper-mass limit is imposed when filling the IMF. The effect is greatest when modelling the observed H(alpha) and FUV star-formation rate ratios in galaxies. This is because mass transfer and merging of stars owing to binary evolution creates more massive stars and stars that have greater mass than the initial maximum imposed on the stellar population.

Radio data and synchrotron emission in consistent cosmic ray models [Replacement]

astro-ph — Thu, 02 Feb 2012 01:34:51 +0000

It is well established that phenomenological two-zone diffusion models of the galactic halo can very well reproduce cosmic-ray nuclear data and the observed antiproton flux. Here, we consider lepton propagation in such models and compute the expected galactic population of electrons, as well as the diffuse synchrotron emission that results from their interaction with galactic magnetic fields. We find models in agreement not only with cosmic ray data but also with radio surveys at essentially all frequencies. Requiring such a globally consistent description strongly disfavors very large ($L\gtrsim 15$ kpc) and, even stronger, small ($L\lesssim 1$ kpc) effective diffusive halo sizes. This has profound implications for, e.g., indirect dark matter searches.

Relativistic collapse and explosion of rotating supermassive stars with thermonuclear effects [Replacement]

astro-ph — Thu, 02 Feb 2012 01:34:30 +0000

We present results of general relativistic simulations of collapsing supermassive stars with and without rotation using the two-dimensional general relativistic numerical code Nada, which solves the Einstein equations written in the BSSN formalism and the general relativistic hydrodynamics equations with high resolution shock capturing schemes. These numerical simulations use an equation of state which includes effects of gas pressure, and in a tabulated form those associated with radiation and the electron-positron pairs. We also take into account the effect of thermonuclear energy released by hydrogen and helium burning. We find that objects with a mass of 5×10^{5} solar mass and an initial metallicity greater than Z_{CNO}~0.007 do explode if non-rotating, while the threshold metallicity for an explosion is reduced to Z_{CNO}~0.001 for objects uniformly rotating. The critical initial metallicity for a thermonuclear explosion increases for stars with mass ~10^{6} solar mass. For those stars that do not explode we follow the evolution beyond the phase of black hole formation. We compute the neutrino energy loss rates due to several processes that may be relevant during the gravitational collapse of these objects. The peak luminosities of neutrinos and antineutrinos of all flavors for models collapsing to a BH are ~10^{55} erg/s. The total radiated energy in neutrinos varies between ~10^{56} ergs for models collapsing to a BH, and ~10^{45}-10^{46} ergs for models exploding.

Signatures of very high energy physics in the squeezed limit of the bispectrum from the field theoretical approach [Replacement]

astro-ph — Thu, 02 Feb 2012 01:34:17 +0000

We investigate the signatures, in the squeezing limit of the primordial scalar bispectrum, of modifications of the standard theory at high energy, such as a modified quantum vacuum or modified dispersion relations, reflecting the effects of different physics at higher energies/earlier times. Our results are obtained through the analysis in field theory and not using the (approximated) templates for the bispectrum. In this way we can obtain the precise dependence on the probed scale and quantify the presence of enhancements and/or non-local shape of the non-Gaussianities, which are relevant, for example, for measurements of the halo bias. It is shown that the signatures are distinctive and can be determined in general, and the results are different from those obtained using the templates proposed in the literature, where existing, in particular because of the interplay between the scale of the observations and the scale of the high-energy physics when taking the large-scale (squeezed) limit. Several pieces of information regarding high energy physics could be obtained in case of detection of these signals, especially bounds on the scales of new physics.

The Universal Gas Mass Fraction in Clusters of Galaxies [Replacement]

astro-ph — Thu, 02 Feb 2012 01:34:00 +0000

We obtained a deep 150ksec Chandra observation of the optically selected cluster of galaxies, RCS 2318+0034, to investigate the gas mass fraction in this system. Combining our deep {\it Chandra} observation with an archival 50ksec observation, we derive gas mass fractions of fgas=0.06 +- 0.02 and 0.10 +- 0.02 within r2500 and r500, respectively. The gas mass fraction in RCS 2318+0034 within r500 is typical of X-ray selected clusters. Further study shows that the large scale properties of RCS 2318+0034, including the relations between gas mass, X-ray luminosity and gas temperature are also consistent with the observed correlations of X-ray selected clusters. However, the gas mass fraction within r2500 is less than most X-ray selected clusters, as previously reported. The deep Chandra image of RCS 2318+0034 shows that this system is presently undergoing a major merger which may have an impact on the inferred gas mass fraction within r2500.

Detection of intrinsic cluster alignments to 100 Mpc/h in the SDSS [Replacement]

astro-ph — Thu, 02 Feb 2012 01:33:50 +0000

We measure the large-scale intrinsic alignments of galaxy clusters in the Sloan Digital Sky Survey (SDSS) using subsets of two cluster catalogues: 6625 clusters with 0.1

Fast Reconnection and Reconnection Diffusion: Implications for Star Formation [Replacement]

astro-ph — Thu, 02 Feb 2012 01:33:37 +0000

Fast reconnection of magnetic field in turbulent fluids allows magnetic field to change its topology and connections. As a result, the traditional concept of magnetic fields being frozen into the plasma is no longer applicable. The diffusion of plasmas and magnetic field is enabled by reconnection and therefore is termed “reconnection diffusion”. We explore the consequences of reconnection diffusion for star formation. In the paper we explain the physics of reconnection diffusion both from macroscopic and microscopic points of view. We quantify the reconnection diffusion rate both for weak and strong MHD turbulence and address the problem of reconnection diffusion acting together with ambipolar diffusion. In addition, we provide a criterion for correctly representing the magnetic diffusivity in simulations of star formation. We show that the role of the plasma effects is limited to “breaking up lines” on small scales and does not affect the rate of reconnection diffusion. We address the existing observational results and demonstrate how reconnection diffusion can explain the puzzles presented by observations, in particular, the observed higher magnetization of cloud cores in comparison with the magnetization of envelopes. We also outline a possible set of observational tests of the reconnection diffusion concept and discuss how the application of the new concept changes our understanding of star formation and its numerical modeling. Finally, we outline the differences of the process of reconnection diffusion and the process of accumulation of matter along magnetic field lines that is frequently invoked to explain the results of numerical simulations

A Successful Broad-band Survey for Giant Lya Nebulae I: Survey Design and Candidate Selection [Replacement]

astro-ph — Thu, 02 Feb 2012 01:33:23 +0000

Giant Lya nebulae (or Lya “blobs”) are likely sites of ongoing massive galaxy formation, but the rarity of these powerful sources has made it difficult to form a coherent picture of their properties, ionization mechanisms, and space density. Systematic narrow-band Lya nebula surveys are ongoing, but the small redshift range covered and the observational expense limit the comoving volume that can be probed by even the largest of these surveys and pose a significant problem when searching for such rare sources. We have developed a systematic search technique designed to find large Lya nebulae at 2

The power spectrum from the angular distribution of galaxies in the CFHTLS-Wide fields at redshift ~0.7 [Replacement]

astro-ph — Thu, 02 Feb 2012 01:33:00 +0000

We measure the real-space galaxy power spectrum on large scales at redshifts 0.5 to 1.2 using optical colour-selected samples from the CFHT Legacy Survey. With the redshift distributions measured with a preliminary ~14000 spectroscopic redshifts from the VIMOS Public Extragalactic Redshift Survey (VIPERS), we deproject the angular distribution and directly estimate the three-dimensional power spectrum. We use a maximum likelihood estimator that is optimal for a Gaussian random field giving well-defined window functions and error estimates. This measurement presents an initial look at the large-scale structure field probed by the VIPERS survey. We measure the galaxy bias of the VIPERS-like sample to be b_g=1.38 +- 0.05 (sigma_8=0.8) on scales k<0.2h/mpc averaged over 0.5

A New Method to Quantify X-ray Substructures in Clusters of Galaxies [Replacement]

astro-ph — Thu, 02 Feb 2012 01:32:36 +0000

We present a new method to quantify substructures in clusters of galaxies, based on the analysis of the intensity of structures. This analysis is done in a residual image that is the result of the subtraction of a surface brightness model, obtained by fitting a two-dimensional analytical model (beta-model or S\’ersic profile) with elliptical symmetry, from the X-ray image. Our method is applied to 34 clusters observed by the Chandra Space Telescope that are in the redshift range 0.02

Kepler-20: A Sun-like Star with Three Sub-Neptune Exoplanets and Two Earth-size Candidates [Replacement]

astro-ph — Thu, 02 Feb 2012 01:32:15 +0000

We present the discovery of the Kepler-20 planetary system, which we initially identified through the detection of five distinct periodic transit signals in the Kepler light curve of the host star 2MASSJ19104752+4220194. We find a stellar effective temperature Teff=5455+-100K, a metallicity of [Fe/H]=0.01+-0.04, and a surface gravity of log(g)=4.4+-0.1. Combined with an estimate of the stellar density from the transit light curves we deduce a stellar mass of Mstar=0.912+-0.034 Msun and a stellar radius of Rstar=0.944^{+0.060}_{-0.095} Rsun. For three of the transit signals, our results strongly disfavor the possibility that these result from astrophysical false positives. We conclude that the planetary scenario is more likely than that of an astrophysical false positive by a factor of 2e5 (Kepler-20b), 1e5 (Kepler-20c), and 1.1e3 (Kepler-20d), sufficient to validate these objects as planetary companions. For Kepler-20c and Kepler-20d, the blend scenario is independently disfavored by the achromaticity of the transit: From Spitzer data gathered at 4.5um, we infer a ratio of the planetary to stellar radii of 0.075+-0.015 (Kepler-20c) and 0.065+-0.011 (Kepler-20d), consistent with each of the depths measured in the Kepler optical bandpass. We determine the orbital periods and physical radii of the three confirmed planets to be 3.70d and 1.91^{+0.12}_{-0.21} Rearth for Kepler-20b, 10.85 d and 3.07^{+0.20}_{-0.31} Rearth for Kepelr-20c, and 77.61 d and 2.75^{+0.17}_{-0.30} Rearth for Kepler-20d. From multi-epoch radial velocities, we determine the masses of Kepler-20b and Kepler-20c to be 8.7\+-2.2 Mearth and 16.1+-3.5 Mearth, respectively, and we place an upper limit on the mass of Kepler-20d of 20.1 Mearth (2 sigma).

Total Hadronic Cross Section and the Elastic Slope: An Almost Model-Independent Connection [Replacement]

astro-ph — Thu, 02 Feb 2012 01:32:06 +0000

An almost model-independent parametrization for the ratio of the total cross section to the elastic slope, as function of the center of mass energy, is introduced. The analytical result is based on the approximate relation of this quantity with the ratio $R$ of the elastic to total cross section and empirical fits to the $R$ data from proton-proton scattering above 10 GeV, under the conditions of asymptotic unitarity and the black-disk limit. This parametrization may be useful in studies of extensive air showers and the determination of the proton-proton total cross section from proton-air production cross section in cosmic-ray experiments.

Solving systems of transcendental equations involving the Heun functions [Replacement]

astro-ph — Thu, 02 Feb 2012 01:31:53 +0000

The Heun functions have wide application in modern physics and are expected to succeed the hypergeometrical functions in the physical problems of the 21st century. The numerical work with those functions, however, is complicated and requires filling the gaps in the theory of the Heun functions and also, creating new algorithms able to work with them efficiently. We propose a new algorithm for solving a system of two nonlinear transcendental equations with two complex variables based on the M\”uller algorithm. The new algorithm is particularly useful in systems featuring the Heun functions and for them, the new algorithm gives distinctly better results than Newton’s and Broyden’s methods. As an example for its application in physics, the new algorithm was used to find the quasi-normal modes (QNM) of Schwarzschild black hole described by the Regge-Wheeler equation. The numerical results obtained by our method are compared with the already published QNM frequencies and are found to coincide to a great extent with them. Also discussed are the QNM of the Kerr black hole, described by the Teukolsky Master equation.

Protoplanetary Disks of T Tauri Binary Systems in the Orion Nebula Cluster [Replacement]

astro-ph — Thu, 02 Feb 2012 01:31:41 +0000

We present a study of protoplanetary disks in spatially resolved low-mass binary stars in the Orion Nebula Cluster (ONC) to assess the impact of binarity on the properties of circumstellar disks. This is currently the largest such study in a clustered high-stellar-density star-forming environment. We particularly aim to determine the presence of magnetospheric accretion and dust disks for each binary component, and measure the overall disk frequency. We carried out spatially resolved adaptive-optics-assisted observations to acquire near-IR photometry and spectroscopy of 26 binaries in the ONC, and determine stellar parameters such as effective temperatures, spectral types, luminosities, and masses, as well as accretion properties and near-infrared excesses for the individual binary components. A fraction of 40(+10/-9)% of the binary components in the sample can be inferred to be T Tauri stars possessing an accretion disk, marginally fewer than the disk fraction of single stars. We find that disks in wide binaries of >200AU separation are consistent with random pairing, while the evolution of circumprimary and circumsecondary disks is observed to be synchronized in close binaries (separations <200AU). Circumbinary disks appear to be unsuitable to explain this difference. Furthermore, we identify several mixed pairs of accreting and non-accreting components, suggesting that these systems are common and that there is no preference for either the more or less massive component to evolve faster. The derived accretion luminosities and mass accretion rates of the ONC binary components are of similar magnitude as those for both ONC single stars and binaries in the Taurus star-forming region. The paper concludes with a discussion of the (presumably weak) connection between the presence of inner accretion disks in young binary systems and the existence of planets in stellar multiples.(abridged)

The relative significance of the H-index [Replacement]

astro-ph — Thu, 02 Feb 2012 01:31:30 +0000

Use of the Hirsch-index ($h$) as measure of an author’s visibility in the scientific literature has become popular as an alternative to a gross measure like total citations (c). I show that, at least in astrophysics, $h$ correlates tightly with overall citations. The mean relation is $h=0.5(\sqrt c+1)$. Outliers are few and not too far from the mean, especially if `normalized’ ADS citations are used for $c$ and $h$. Whatever the theoretical reasoning behind it, the Hirsch index in practice does not appear to measure something significantly new.

Leading Relativistic Corrections to the Kompaneets Equation [Replacement]

astro-ph — Thu, 02 Feb 2012 01:31:05 +0000

We calculate the first relativistic corrections to the Kompaneets equation for the evolution of the photon frequency distribution brought about by Compton scattering. The Lorentz invariant Boltzmann equation for electron-photon scattering is first specialized to isotropic electron and photon distributions, the squared scattering amplitude and the energy-momentum conserving delta function are each expanded to order v^/c^4, averages over the directions of the electron and photon momenta are then carried out, and finally an integration over the photon energy yields our Fokker- Planck equation. The Kompaneets equation, which involves only first- and second-order derivatives with respect to the photon energy, results from the order v^2/c^2 terms, while the first relativistic corrections of order v^4/c^4 introduce third- and fourth-order derivatives. We emphasize that our result holds when neither the electrons nor the photons are in thermal equilibrium; two effective temperatures characterize a general, non-thermal electron distribution. When the electrons are in thermal equilibrium our relativistic Fokker-Planck equation is in complete agreement with the most recent published results, but we both disagree with older work.

Analyzing Cosmic Bubble Collisions

claudia43 — Wed, 01 Feb 2012 14:55:45 +0000

Roberto Gobbetti, Matthew Kleban
http://arxiv.org/pdf/1201.6380v1.pdf

The Milky Way Project First Data Release: A Bubblier Galactic Disk

astro-ph — Wed, 01 Feb 2012 01:59:14 +0000

We present a new catalogue of 5,106 infrared bubbles created through visual classification via the online citizen science website ‘The Milky Way Project’. Bubbles in the new catalogue have been independently measured by at least 5 individuals, producing consensus parameters for their position, radius, thickness, eccentricity and position angle. Citizen scientists – volunteers recruited online and taking part in this research – have independently rediscovered the locations of at least 86% of three widely-used catalogues of bubbles and H ii regions whilst finding an order of magnitude more objects. 29% of the Milky Way Project catalogue bubbles lie on the rim of a larger bubble, or have smaller bubbles located within them, opening up the possibility of better statistical studies of triggered star formation. Also outlined is the creation of a ‘heat map’ of star-formation activity in the Galactic plane. This online resource provides a crowd-sourced map of bubbles and arcs in the Milky Way, and will enable better statistical analysis of Galactic star-formation sites.