The Metal-strong Damped Lya Systems

ABSTRACT. We have identified a metal-strong [ or] damped Lya log N(Zn) ≥ 13.15 log N(Si) ≥ 15.95 (MSDLA) population from an automated quasar (QSO) absorber search in the Sloan Digital Sky Survey (SDSS) Data Release 3 quasar sample and find that MSDLAs comprise ≈5 % of the entire DLA population with found in QSO sight lines with. We have also acquired 27 Keck ESI (Echellete Spectrographz ≥ 2.2 r! 19.5abs and Imager) follow-up spectra of metal-strong candidates in order to evaluate our automated technique and examine the MSDLA candidates at higher resolution. We demonstrate that the rest equivalent widths of strong Zn ii l2026 and Si ii l1808 lines in low-resolution SDSS spectra are accurate indicators of metal-strong systems in higher resolution spectra, and predict the observed equivalent widths and signal-to-noise ratios needed toWobs detect certain extremely weak lines with high-resolution instruments. We investigate how the MSDLAs may affect previous studies concerning a dust obscuration bias and the N(H i)–weighted cosmic mean metallicity. Finally, we include a brief discussion of abundance ratios in our ESI sample and find that underlyingAZ(z)S mostly Type II supernova enrichment are differential depletion effects due to dust (and in a few cases, these are quite strong); we present here a handful of new Ti and Mn measurements, both of which are useful probes of depletion in DLAs. Future papers will present detailed examinations of particularly metal-strong DLAs from high-resolution Keck I HIRES and VLT UVES spectra. Online material: extended table, tar fil