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The CORALS survey I: New estimates of the number density and gas content of damped Lyman alpha systems free from dust bias

Ellison, S. L. and Yan, L. and Hook, I. M. and Pettini, M. and Wall, J. V. and Shaver, P. (2001) The CORALS survey I: New estimates of the number density and gas content of damped Lyman alpha systems free from dust bias. Astronomy & Astrophysics, 379 (2). pp. 393-406. ISSN 0004-6361. doi:10.1051/0004-6361:20011281.

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We present the first results from the Complete Optical and Radio Absorption Line System (CORALS) survey. We have compiled a homogeneous sample of radio-selected QSOs from the Parkes Catalogue and searched for damped Lyman alpha systems (DLAs) towards every target, irrespective of its optical magnitude. This approach circumvents selection effects -particularly from intervening dust -which have long been suspected to affect DLA surveys in optically-selected, magnitude-limited QSO samples. The CORALS data set consists of 66 Z_(em) ≥ 2.2 QSOs in which 22 DLAs with absorption redshifts 1.8 ≤ Z-(abs) ≤ Z_(em) have been identified over a total redshift interval Δz = 55.46. Three of the DLAs are classified as "associated" systems with Z_(abs) ~ Z_(em); of the 19 intervening DLAs, 17 are new discoveries. In this first paper of the CORALS series we describe the sample, present intermediate resolution spectroscopy and determine the population statistics of DLAs. We deduce a value of the neutral gas mass density traced by DLAs (expressed as a fraction of the closure density) logΩ_(DLA)h = -2.59^(+0.17)_(-0.24), and a number density of DLAs per unit redshift n(z) = 0.31^(+0.09)_(-0.08), both at a mean redshift (z). Both values are only marginally higher than those measured in optically selected samples of QSOs. Taking into account the errors, we conclude that dust-induced bias in previous surveys may have led to an underestimate of these quantities by at most a factor of two. While n(z) is greater in fainter (B 〉20) QSOs, the effect is only at the ~1σ level and we have not uncovered a previously unrecognised population of high column density (N(HI) 〉10^(21) (cm^(-2)) DLAs in front of faint QSOs. These conclusions are tentative because of the limited size of our data set; in particular the distribution of column densities is poorly sampled at the high end where a much larger survey of radio-selected QSOs is required the improve the statistics.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Ellison, S. L.0000-0002-1768-1899
Yan, L.0000-0003-1710-9339
Hook, I. M.0000-0002-2960-978X
Pettini, M.0000-0002-5139-4359
Additional Information:© 2001 ESO. Received: 19 June 2001. Accepted: 12 September 2001. It is a pleasure to acknowledge the consistent support of this project by the ESO and AAT Time Assignment Panels and the professional and efficient help of the telescope staff at the AAT, ESO 3.6-m and VLT. In particular, we are grateful to the ESO Paranal science operations staff for their expert execution of our service observations. We thank Mauro Giavalisco and Lisa Storrie-Lombardi for obtaining spectra of two of our targets and Joop Schaye for useful comments on an earlier draft of this paper. The work presented here is based in part on data obtained with the ESO facilities on La Silla (EFOSC/3.6-m) and Paranal (FORS1/UT1).
Group:Infrared Processing and Analysis Center (IPAC)
Subject Keywords:galaxies: quasars: absorption lines - ISM: dust, extinction - galaxies: evolution
Issue or Number:2
Record Number:CaltechAUTHORS:20180226-081547969
Persistent URL:
Official Citation:The CORALS survey I: New estimates of the number density and gas content of damped Lyman alpha systems free from dust bias S. L. Ellison, L. Yan, I. M. Hook, M. Pettini, J. V. Wall and P. Shaver A&A, 379 2 (2001) 393-406 DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:84949
Deposited By: Ruth Sustaita
Deposited On:26 Feb 2018 18:23
Last Modified:15 Nov 2021 20:24

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