COMPARING GALAXIES AND LY-ALPHA ABSORBERS AT LOW-REDSHIFT

A scenario is explored in which Ly alpha absorbers at low redshift ari se from lines of sight through extended galaxy disks, including those of dwarf and low surface brightness galaxies. A population of galaxies is simulated based upon observed distributions of galaxy properties, and the gas disks are modeled using pressure and gravity confinement. Some parameter values are ruled out by comparing simulation results to the observed galaxy luminosity function, and constraints may be made on the absorbing cross sections of galaxies. Simulation results indica te that it is difficult to match absorbers with particular galaxies ob servationally since absorption typically occurs at high-impact paramet ers (>200 kpc) from luminous galaxies. Low-impact parameter absorption is dominated by low-luminosity dwarfs. A large fraction of absorption lines is found to originate from low surface brightness galaxies, so that the absorbing galaxy is likely to be misidentified. Low-redshift Ly alpha absorber counts can easily be explained by moderately extende d galaxy disks when low surface brightness galaxies are included, and it is easily possible to find a scenario that is consistent with the o bserved galaxy luminosity function, with low-redshift Lyman limit abso rber counts, and with standard nucleosynthesis predictions of the bary on density, Omega(B).