Title:

Shadows of Galaxies: Tracing Galaxy Evolution with Damped and
Sub-Damped Lyman-alpha Quasar Absorbers



Varsha Kulkarni
University of South Carolina



Abstract:

Absorption lines in quasar spectra probe interstellar gas in galaxies
at various stages of evolution. They should thus provide powerful
probes of the history of star formation and chemical enrichment in
galaxies. One major obstacle in trying to understand the evolution of
the strong quasar absorption lines known as the damped Lyman-alpha
absorbers (DLAs) has been the small number of metallicity measurements
at redshifts z < 1.5, an epoch spanning 70% of the age of the
Universe. With spectroscopic studies using the Hubble Space Telescope
and several ground-based telescopes, we have recently tripled the DLA
metallicity sample at z < 1.5. Our results suggest a "missing metals
problem" for DLAs, in apparent contradiction with the predictions of
cosmic chemical evolution models. On the other hand, we have
discovered a few highly metal-rich sub-DLA absorber galaxies, with
near-solar or supersolar metallicities 6-9 billion years ago. These
data suggest that sub-DLAs may make a significant contribution to the
cosmic metal budget. We will also discuss the metallicity vs. velocity
dispersion trends for DLAs and sub-DLAs. Finally, we will discuss the
nature of the absorber galaxies and their star formation rates based
on deep optical and near-infrared imaging studies, and the
implications for galaxy evolution.