The metal-strong damped Lyα systems

We have identified a metal-strong [log N(Zn+) >= 13.15 or log N(Si+) >= 15.95] damped Ly alpha (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 approximate to 5% of the entire DLA population with z(abs) >= 2.2found in QSO sight lines with r < 19.5. We have also acquired 27 Keck ESI (Echellete Spectrograph 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 lambda 2026 and Si II lambda 1808 lines in low-resolution SDSS spectra are accurate indicators of metal-strong systems in higher resolution spectra, and predict the observed equivalent widths W-obs and signal-to-noise ratios needed to 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 ((z)). Finally, we include a brief discussion of abundance ratios in our ESI sample and find that underlying 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.