The local Lyman-alpha forest: Relationship of the absorbers to galaxies

I have used pointed galaxy redshift surveys to look for a relationship between the distribution of nearby (cz < 20, 000 km s −1) low column density (12.5 < log N_HI (cm −2) < 14.5) intergalactic Lyα forest absorbers and faint galaxies. The survey has probed sightlines toward 15 bright AGN previously observed with HST and GHRS or STIS spectrograph, and containing a sample of 134 low column density Lyα systems. Deep ground-based optical imaging and spectroscopy have been used to look for galaxies in the sightlines. For the most nearby absorbers, at cz < 3000 kms−1 , galaxies as faint as MB = −12 can be detected close to the line of sight, while for the most distant absorbers (cz ≈ 20, 000 km s−1), galaxies more than a magnitude fainter than L* can are detectable several hundred kpc in projected distance from each sightline. I have failed to find strong evidence of any relationship between Lyα absorbers and the nearest galaxies. Though there seems to be a tendency for some absorbers to be associated with groups of galaxies, I have found little indication that any absorbers are associated with individual galaxies in general. Two cases of close proximity (≤100 kpc) between dwarf galaxies and Lyα absorbers were found, but these must be contrasted with the ≥40 cases where galaxy surveys to similar magnitude limits failed to find nearby galaxies. Four of the regions studied are in galaxy voids as defined by large redshift surveys. I have failed to find even faint galaxies, with −12 < M_B < −14, within these voids. The lack of galaxies coincident with the absorbers in voids has been used to set the fraction of local baryons in the voids at 3.5 ± 1% of the total baryons predicted by Big Bang nucleosynthesis.; While I have discovered a dwarf galaxy toward 3C273 at cz = 1556 km s−1 that might be near enough to the sightline for an associated extended halo of diffuse gas to be causing the absorption, in general I have found no strong evidence that Lyα absorbers are the result of such halos. However, I have found several groups of galaxies near absorbers. One is toward PKS2155−304 and two more, one reported here for the first time, are toward 3C273 and Q1230+011. In total, I have discovered 16 galaxies coincident with 12 Lyα absorbers, where “coincident” means that the galaxies have redshifts within ±300 km s−1 of the absorber.; In addition to the observational work, a simple model of wind production by dwarf galaxies via strong outflows from supernovae and massive stars is presented. (Abstract shortened by UMI.)...