Neutral hydrogen optical depth near star-forming galaxies at z~2.4 in the Keck Baryonic Structure Survey
(19 votes over all institutions)
[Abridged] We study the interface between galaxies and the intergalactic medium by measuring the absorption by neutral hydrogen in the vicinity of star-forming galaxies at z~2.4. Our sample consists of 679 rest-frame-UV selected galaxies with spectroscopic redshifts that have impact parameters 3 sigma level) out to at least 2.8 Mpc (i.e. > 9 comoving Mpc). We detect two types of redshift space anisotropies. On scales < 200 km/s, or 3 sigma significance), which we attribute to large-scale infall (i.e. the Kaiser effect). Within 100 (200) kpc, and over \pm 165 km/s, the covering fraction of gas with Ly-a optical depth greater than unity is 100(+0)(-32)% (86(+14)(-18)%). Absorbers with tau(Ly-a)> 0.1 are typically closer to galaxies than random. The mean galaxy overdensity around absorbers increases with the optical depth and also as the length scale over which the galaxy overdensity is evaluated is decreased. Absorbers with tau(Ly-a)~1 reside in regions where the galaxy number density is close to the cosmic mean on scales > 0.25 Mpc.
