Simulations of Lyα absorption and the low redshift galaxy population

Abstract

Understanding galaxy evolution will require knowledge of the properties of the low redshift galaxy population. Many nearby galaxies are difficult to detect in optical surveys because they are low in surface brightness. Furthermore, the gaseous extent of galaxies has not been well constrained due to the possible presence of ionized gas beyond where galaxy disks are seen to cut off in 21 cm maps. UV observations of Lyα absorption along quasar lines of sight therefore allow for an especially powerful probe of gas in galaxies. I show that it is possible to simulate a population of galaxies at low redshift which is consistent with galaxy observations, explains low redshift Lyα absorber counts, and is consistent with the baryon density as predicted by standard big bang nucleosynthesis. By comparing simulation results with observed galaxy luminosity functions, an upper limit can be found for the characteristic absorbing cross section of galaxies.