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arXiv · 1609.09081

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

T. A. M. Berg·S. L. Ellison·J. X. Prochaska·R. Sanchez-Ramirez·S. Lopez·V. D'Odorico·G. Becker·L. Christensen·G. Cupani·K. Denney·G. Worseck
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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.

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T. A. M. Berg, S. L. Ellison, J. X. Prochaska, R. Sanchez-Ramirez, S. Lopez, V. D'Odorico, G. Becker, L. Christensen, G. Cupani, K. Denney, G. Worseck. 2016-09-28. On the selection of damped Lyman alpha systems using MgII absorption at 2<z<4. https://doi.org/10.1093/mnrasl/slw185

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