Comparing Low Surface Brightness Galaxies and Ly$α$ Absorbers

Abstract

I explore the hypothesis that Ly$α$ absorption at low redshift is caused by the outer regions of extended galaxy disks, including those of dwarf and low surface brightness galaxies. McGaugh (1996) has shown that the distribution of central galaxy surface brightnesses may be flat to 25 B mag arcsec$^{-2}$ or fainter. A population of galaxies is simulated based upon observed distributions. The low-redshift neutral column density distribution is predicted, and an estimate is made for the number density of disk galaxies required to explain all absorbers. Results relating to galaxy luminosities and impact parameters are discussed.