Measuring Feedback in Damped Lyman Alpha Systems

We measure feedback (heating rates) in damped Lyman alpha systems from the cooling rate of the neutral gas. Since cooling occurs through [C II] 158 micron emission, we infer cooling from C II^{*} 1335.7 absorption lines detected with HIRES on the Keck I telescope. The inferred heating rates are about 30 times lower than for the Galaxy ISM. At z = 2.8, the implied star formation rate per unit area is 10^{-2.4+-0.3} solar masses per kpc^{2} per year, and the the star formation rate per unit comoving volume is 10^{-0.8+-0.2} solar masses per Mpc^{3} per year. This is the first measurement of star formation rates in objects likely to be the progenitors of current galaxies.Comment: 7 pages, 5 figures, Proceedings of the ESO/ECF/STScI Workshop on Deep Field

Chemical Abundances of the Damped Lya Systems at z>1.5

We present chemical abundance measurements for 19 damped lya systems observed with HIRES on the 10m W.M. Keck Telescope. Our principal goal is to investigate the abundance patterns of the damped systems and thereby determine the underlying physical processes which dominate their chemical evolution. We place particular emphasis on gauging the relative importance of two complementary effects often invoked to explain the damped lya abundances: (1) nucleosynthetic enrichment from Type II supernovae and (2) an ISM-like dust depletion pattern. Similar to the principal results of Lu et al. (1996), our observations lend support both for dust depletion and Type II SN enrichment. Specifically, the observed overabundance of Zn/Fe and underabundance of Ni/Fe relative to solar abundances suggest significant dust depletion within the damped lya systems. Meanwhile, the relative abundances of Al, Si, and Cr vs. Fe are consistent with both dust depletion and Type II supernova enrichment. Our measurements of Ti/Fe and the Mn/Fe measurements from Lu et al. (1996), however, cannot be explained by dust depletion and indicate an underlying Type II SN pattern. Finally, the observed values of [S/Fe] are inconsistent with the combined effects of dust depletion and the nucleosynthetic yields expected for Type II supernovae. This last result emphasizes the need for another physical process to explain the damped lya abundance patterns. We also examine the metallicity of the damped lya systems both with respect to Zn/H and Fe/H. Our results confirm previous surveys by Pettini and collaborators, i.e., [] = -1.15 +/- 0.15 dex. [abridged]Comment: 18 pages, 4 embedded figures, 20 additional figures. Accepted to the Astrophysical Journal 10/20/98. Uses Latex2e, emualteapj.sty, and onecolfloat.st