A high molecular fraction in a subdamped absorber at z = 0.56

Neil H. M. Crighton, Jill Bechtold, Robert F. Carswell, Romeel Davé, Craig B. Foltz, Buell T. Jannuzi, Simon L. Morris, John M. O'Meara, J. Xavier Prochaska, Joop Schaye, Nicolas Tejos

Research output: Contribution to journalArticlepeer-review

Abstract / Description of output

Measuring rest-frame ultraviolet rotational transitions from the Lyman and Werner bands in absorption against a bright background continuum is one of the few ways to directly measure molecular hydrogen (H2). Here, we report the detection of absorption from H2 at z = 0.56 in a subdamped Lyα system with neutral hydrogen column density NHI = 1019.5 ± 0.2 cm-2. This is the first H2 system analysed at a redshift of -1.93 ± 0.36 based on modelling the line profiles, with a robust model-independent lower limit of fH2 > 10-3. This is higher than fH2 values seen along sightlines with similar NHI through the Milky Way disc and the Magellanic Clouds. The metallicity of the absorber is 0.19+0.21-0.10 solar, with a dust-to-gas ratio of
Original languageEnglish
Pages (from-to)178-193
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
Publication statusPublished - 27 May 2013

Keywords / Materials (for Non-textual outputs)

  • ISM: molecules
  • galaxies: haloes
  • quasars: absorption lines


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