Keck ESI Observations of Metal-Poor Damped Lyman-{\alpha} Systems
  We present the first results from a survey of SDSS quasars selected for
strong H I damped Lyman-{\alpha} (DLA) absorption with corresponding low
equivalent width absorption from strong low-ion transitions (e.g. C II
{\lambda}1334 and Si II {\lambda}1260). These metal-poor DLA candidates were
selected from the SDSS DR5 quasar spectroscopic database, and comprise a large
new sample for probing low metallicity galaxies. Medium-resolution echellette
spectra from the Keck ESI spectrograph for an initial sample of 35 systems were
obtained to explore the metal-poor tail of the DLA distribution and to
investigate the nucleosynthetic patterns at these metallicities. We have
estimated saturation corrections for the moderately under-resolved spectra, and
systems with very narrow Doppler parameter (b \le 5 km s-1) will likely have
underestimated abundances. For those systems with Doppler parameters b > 5 km
s-1, we have measured low metallicity DLA gas with [X/H] < -2.4 for at least
one of C, O, Si, or Fe. Assuming non-saturated components, we estimate that
several DLA systems have [X/H] < -2.8, including five DLA systems with both low
equivalent widths and low metallicity in transitions of both C II and O I. All
of the measured DLA metallicities, however, exceed or are consistent with a
metallicity of at least 1/1000 of solar, regardless of the effects of
saturation in our spectra. Our results indicate that the metal-poor tail of
galaxies at z \sim 3 drops exponentially at [X/H]< -3. The observed ratio of
[C/O] for values of [O/H] < -2.5 exceeds values seen in moderate metallicity
DLA systems, and also exceeds theoretical nucleosynthesis predictions for
higher mass Population III stars.
