Galactic chemical abundances at z > 3. I. First results from the Echellette Spectrograph and Imager

We present the first results from an ongoing survey to discover and measure the metallicity of z > 3 damped Ly alpha systems with the Echellette Spect rograph and Imager (ESI) on the Keck II telescope. Our motivation arises fr om a recent study on damped Ly alpha systems suggesting only mild evolution in the cosmic metallicity from z similar to 2 to 4. The Echellette Spectro graph and Imager, which provides two complementary spectroscopic modes, is the ideal instrument for a z > 3 damped Ly alpha survey. We describe our ob serving strategy and report on the discovery and analysis of five new z > 3 damped Ly alpha systems acquired in a single night of observing. These obs ervations further support the principal conclusions of the previous study: (1) the cosmic metallicity in neutral gas inferred from the damped Ly alpha systems does not evolve significantly from z similar to 2 to 4; (2) the un weighted metallicity exhibits a statistically significant decrease with inc reasing redshift; and (3) not a single damped Ly alpha system has a metalli city below [Fe/H] = -3. We discuss the implications of these results and co mment on recent theoretical studies that attempt to explain the observation s.