Towards A Complete Picture of Damped Lyman Alpha Systems

Eric Gawiser
Univ of California San Diego

Damped Lyman alpha absorption systems (DLAs) contain most of
the neutral hydrogen in the high-redshift universe and are the likely
progenitors of typical galaxies like the Milky Way.  Nonetheless, it is not yet 
clear if DLAs are massive galaxies or low-mass protogalaxies, or whether 
they are similar to the Lyman break galaxies or represent a separate
population.  I will present results from our observational program
designed to clarify the DLA picture.  Neither the fraction of critical
density comprised by neutral hydrogen nor the metallicity of the universe
as probed by DLAs evolves from z=4 to z=2.  Dust extinction does not
appear to bias these measurements significantly.  The cosmic star
formation rate measured in DLAs is comparable to that of Lyman break
galaxies although considerably weaker on a system-by-system basis.
Finally, I will describe an ongoing effort to determine the mass of DLAs
by studying their cross-correlation with Lyman break galaxies.