On the selection of damped Lyman α systems using Mg II absorption at 2 < zabs < 4
Date Issued
2017
Author(s)
Berg, T. A. M.
•
Ellison, S. L.
•
Prochaska, J. X.
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Sánchez-Ramírez, R.
•
Lopez, S.
•
•
Becker, G.
•
Christensen, L.
•
•
Denney, K.
•
Worseck, G.
Abstract
The XQ-100 survey provides optical and near-infrared coverage of 36 blindly selected, intervening damped Lyman α systems (DLAs) at 2 < zabs < 4, simultaneously covering the Mg II doublet at λλ2796, 2803Å, and the Ly α transition. Using the XQ-100 DLA sample, we investigate the completeness of selecting DLA absorbers based on their Mg II rest-frame equivalent width (W0^{2796}) at these redshifts. Of the 29 DLAs with clean Mg II profiles, we find that six (20 per cent of DLAs) have W0^{2796} < 0.6 Å. The DLA incidence rate of W0^{2796} < 0.6 Å absorbers is a factor of ∼5 higher than what is seen in z ∼ 1 samples, indicating a potential evolution in the Mg II properties of DLAs with redshift. All of the W0^{2796} < 0.6 Å DLAs have low metallicities (-2.5 < [M/H] < -1.7), small velocity widths (v90 < 50 km s-1), and tend to have relatively low N(H I). We demonstrate that the exclusion of these low W0^{2796} DLAs results in a higher mean N(H I) which in turn leads to an ∼7 per cent increase in the cosmological gas density of H I of DLAs at 2 < zabs < 4; and that this exclusion has a minimal effect on the H I-weighted mean metallicity.
Volume
464
Issue
1
Start page
L56
Issn Identifier
0035-8711
Ads BibCode
2017MNRAS.464L..56B
Rights
open.access
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