Dr. Varsha Kulkarni
Univ. South Carolina

University of Florida Astronomy Colloquium - Feb. 21st, 2007

Shadows of Galaxies: Tracing Galaxy Evolution with Quasar Absorption Lines

The evolution of galaxies and the cosmic history of element production are fundamental themes in modern astrophysics and cosmology. 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. Recently, in spectroscopic studies with the Hubble Space Telescope and several ground-based telescopes, we have nearly 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 recently discovered a few highly metal-rich sub-DLA absorber galaxies, including a galaxy with highly supersolar metallicity 6 billion years ago. We discuss the role of the sub-DLAs in the cosmic metal budget. Finally, we 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.