The Metal-Strong Damped Lyman-alpha Systems

Abstract

We have identified a metal-strong (logN(Zn+) > 13.15 or logN(Si+) > 15.95) DLA (MSDLA) population from an automated quasar (QSO) absorber search in the Sloan Digital Sky Survey Data Release 3 (SDSS-DR3) quasar sample, and find that MSDLAs comprise ~5% of the entire DLA population with z_abs > 2.2 found in QSO sightlines with r < 19.5. We have also acquired 27 Keck ESI follow-up spectra of metal-strong candidates to evaluate our automated technique and examine the MSDLA candidates at higher resolution. We demonstrate that the rest equivalent widths of strong ZnII 2026 and SiII 1808 lines in low-resolution SDSS spectra are accurate metal-strong indicators for higher-resolution spectra, and predict the observed equivalent widths 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(HI)-weighted cosmic mean metallicity <Z(z)>. Finally, we include a brief discussion of abundance ratios in our ESI sample and find that underlying mostly Type II supernovae enrichment are differential depletion effects due to dust (and in a few cases 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 KeckI/HIRES and VLT/UVES spectra.

Accepted to the PASP; 20 pages, 14 figures, 6 tables

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• Dust-depletion sequences in damped Lyman-α absorbers: a unified picture from low-metallicity systems to the Galaxy
• A New Measurement of the Temperature Density Relation of the IGM From Voigt Profile Fitting
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• The Magellan Uniform Survey of Damped Lyman alpha Systems I: Cosmic Metallicity Evolution
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• The chemical compositions of 10 new sub-DLAs and strong Lyman-limit systems at z < 1.5
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• Precise limits on cosmological variability of the fine-structure constant with zinc and chromium quasar absorption lines
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• An integral field spectroscopic survey for high redshift damped Lyman-alpha galaxies
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• On the Absence of High Metallicity-High Column Density Damped Lyman Alpha Systems: Molecule Formation in a Two-Phase Interstellar Medium
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• A Metal-Strong and Dust-Rich Damped \lya Absorption System toward the Quasar SDSS J115705.52+615521.7
• Emergence of a Quasar Outflow
• Ionization corrections in a multi-phase interstellar medium: Lessons from a z~2 sub-DLA
• The host galaxies of strong CaII QSO absorption systems at z<0.5
• Where are the Cosmic Metals at z~3?
• Probing feedback in protogalaxies: Multiphase gas in a DLA at z~2.4
• Dust depletion, chemical uniformity and environment of CaII H&K quasar absorbers
• A quasar hiding behind two dusty absorbers. Quantifying the selection bias of metal-rich, damped Lyman-alpha absorption systems
• Metallicities and dust content of proximate damped Lyman alpha systems in the Sloan Digital Sky Survey
• Quasar 2175 Å dust absorbers I: metallicity, depletion pattern, and kinematics
• Interstellar Ti II in the Milky Way and Magellanic Clouds
• The most metal-rich damped Lyman alpha systems at z>1.5 I: The Data
• Evidence of Pop~III stars' chemical signature in neutral gas at z~6. A study based on the E-XQR-30 spectroscopic sample
• Quasar 2175 Å dust absorbers II: Correlation analysis and relationship with other absorption line systems
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