Effects of Galaxy Selection Upon Lyman Alpha Absorber Identification

Abstract

While it is possible to explain Lyman alpha absorber counts at low redshift using gas which is associated with moderately extended galaxies (Linder 1997), absorbers are often observed to be associated with galaxies at larger impact parameters from quasar lines of sight than are expected from calculated galaxy absorption cross sections in such absorber-galaxy models. However, a large fraction of absorbers is expected to arise in lines sight through galaxies which are low in luminosity and/or surface brightness, so that they are unlikely to be detected in surveys for galaxies close to quasar lines of sight. Given that it is impossible to be certain that any particular absorber has been matched to the correct galaxy, I show that it is possible to simulate plots of absorption covering factors around luminous galaxies which resemble observed plots by assuming that absorption often originates in unidentified galaxies.