A Comparative Study of Damped Lyman Alpha Galaxies

Abstract

We compare the properties of a sample of local (z=0) gas-rich galaxies studied in 21 cm emission to a sample of 13 low-redshift (z < 1) damped Lyman alpha (DLA) galaxies identified as the counterparts of low-redshift DLA systems found in QSO absorption-line surveys. This absorption-selected sample has average redshift <z> = 0.5. We find that many of the properties of the two samples are comparable. However, consideration of the statistical results on all known low-redshift DLA systems indicates that there is: (1) a somewhat higher incidence and cosmological mass density for the low-redshift DLA systems in comparison to expectations at z=0 and (2) an unexpectedly high rate of occurrence of very large column density [N(HI) > 1E21 atoms/cm^2] low-redshift DLA systems; both of these results are discussed by Rao & Turnshek in these proceedings. These differences, coupled with imaging studies, suggest that there may be an excess of low-redshift DLA galaxies in the form of dwarf and/or low surface brightness galaxies. Some examples of low-redshift DLA galaxies are shown by Nestor et al. in these proceedings.