Keck Echellette Spectrograph and Imager observations of metal-poor damped Lyα systems

Abstract

We present the first results from a survey of SDSS quasars selected for strong HI damped Lyα (DLA) absorptionwith corresponding low equivalent width absorption from strong low-ion transitions (e.g., C II λ1334 and SiII λ1260). These metal-poor DLA candidates were selected from the SDSS fifth release quasar spectroscopic database, and comprise a large new sample for probing low-metallicity galaxies. Medium-resolution echellette spectra from the Keck Echellette Spectrograph and Imager 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 underresolved spectra, and systems with very narrow Doppler parameters (b ≤ 5 km s-1) will likely have underestimated abundances. For those systems with Doppler parameters b>5 kms-1,we havemeasured low-metallicity DLA gas with [X/H] < -4.0 are extremely rare, and could comprise only 8 × 10-7 of DLA systems. The relative abundances of species within these low-metallicity DLA systems are compared with stellar nucleosynthesis models, and are consistent with stars having masses of 30M⊙ < M* < 100M⊙. The observed ratio of [C/O] for values of [O/H]