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Session 115 - Galaxies and Clusters of Galaxies.
Oral session, Thursday, January 16
Frontenac Ballroom,
I explore the possibility that low redshift Ly\alpha absorption arises mostly from lines of sight through extended galaxy disks. Low surface brightness galaxies, which may be relatively abundant, are usually found to be gas rich and therefore must make some contribution to Ly\alpha absorption. Galaxy disks are observed to have sharp cutoffs in 21 cm maps which have been explained by a rapid increase in the ionization level. Low column density absorption may arise in the ionized outer regions of the disks, while Lyman limit systems could be observed from the region of changing ionization. A population of galaxies is simulated based upon observed distributions and modeled using pressure and gravity confinement. The number density of disk galaxies is constrained using absorber counts, and the low redshift neutral column density distribution is predicted for various parameter values. It may be difficult to match absorbers with particular galaxies observationally since absorption typically occurs at high impact parameters (>300 kpc) from luminous galaxies. Low impact parameter absorption is dominated by dwarfs. Overall, absorption can be explained by a combination of luminous galaxies, which have large cross sections, and dwarfs, which are high in number density.
