The covering factor of high-redshift damped Lyman-α systems

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  • N. Kanekar
    1National Radio Astronomy Observatory, 1003 Lopezville Road, Socorro, NM 87801, USA
  • W. M. Lane
    2Naval Research Laboratory, Code 7213, 4555 Overlook Ave SW, Washington, DC 20375, USA
  • E. Momjian
    1National Radio Astronomy Observatory, 1003 Lopezville Road, Socorro, NM 87801, USA
  • F. H. Briggs
    3Australian National University, Weston, ACT 2611, Australia
  • J. N. Chengalur
    4National Centre for Radio Astrophysics, Ganeshkhind, Pune, 411007, India

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<jats:title>Abstract</jats:title> <jats:p>We have used the Very Long Baseline Array to image 18 quasars with foreground damped Lyman-α systems (DLAs) at 327, 610 or 1420 MHz, to measure the covering factor f of each DLA at or near its redshifted H i 21 cm line frequency. Including six systems from the literature, we find that none of 24 DLAs at 0.09 &lt; z &lt; 3.45 has an exceptionally low covering factor, with f∼ 0.45–1 for the 14 DLAs at z &gt; 1.5 and f∼ 0.41–1 for the 10 systems at z &lt; 1, and consistent covering factor distributions in the two subsamples. The observed paucity of detections of H i 21 cm absorption in high-z DLAs thus cannot be explained by low covering factors and is instead likely to arise due to a larger fraction of warm H i in these absorbers.</jats:p>

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