On the selection of damped Lyman alpha systems using MgII absorption at 2<z<4

Abstract

The XQ-100 survey provides optical and near infrared coverage of 36 blindly selected, intervening damped Lyman alpha systems (DLAs) at 2 < z < 4, simultaneously covering the MgII doublet at 2796A, 2803A, and the Ly-alpha transition. Using the XQ-100 DLA sample, we investigate the completeness of selecting DLA absorbers based on their MgII rest-frame equivalent width (W2796) at these redshifts. Of the 29 DLAs with clean MgII profiles, we find that six (20% of DLAs) have W2796 < 0.6A. The DLA incidence rate of W2796 < 0.6A absorbers is a factor of ~5 higher than what is seen in z~1 samples, indicating a potential evolution in the MgII properties of DLAs with redshift. All of the W2796 < 0.6A DLAs have low metallicities (-2.5 < [M/H] < -1.7), small velocity widths (v90 < 50 km/s), and tend to have relatively low N(HI). We demonstrate that the exclusion of these low W2796 DLAs results in a higher mean N(HI) which in turn leads to a ~7% increase in the cosmological gas density of HI of DLAs at 2 < z < 4; and that this exclusion has a minimal effect on the HI-weighted mean metallicity.

Accepted into MNRAS Letters. 6 pages, 2 figures

References in corpus (10)

• On the (Non)Evolution of HI Disks over Cosmic Time
• Metallicity Evolution of Damped Lyman-alpha Systems out to z~5
• Velocity-Metallicity Correlation for high-z DLA Galaxies: Evidence for a Mass-Metallicity Relation?
• The Neutral Hydrogen Cosmological Mass Density at z=5
• The Role of Sub-damped Lyman-alpha Absorbers in the Cosmic Evolution of Metals
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• The connection between metallicity and metal-line kinematics in (sub-)damped Lyman-alpha systems
• Chemical abundances of damped Lyman alpha systems in the XQ-100 survey
• Revisiting the origin of the high metallicities of sub-damped Lyman-alpha systems
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• Evidence of First Stars-enriched Gas in High-redshift Absorbers
• The evolution of neutral hydrogen over the past 11 Gyr via HI 21 cm absorption
• Strong Mg II and Fe II Absorbers at 2.2 < z < 6.0
• Sub-damped Lyman alpha systems in the XQ-100 survey II -- Chemical evolution at 2.4<z<4.3
• Solving the conundrum of intervening strong MgII absorbers towards GRBs and quasars
• MUSE-ALMA Haloes IX: Morphologies and Stellar Properties of Gas-rich Galaxies
• The Qz5 Survey (I): How the HI Mass Density of the Universe Evolves With Cosmic Time
• Ultra-strong MgII absorbers trace both inflowing and outflowing gas: insights from dual down-the-barrel and quasar sightlines