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

Research output: Contribution to journalArticle

  • 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

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Original languageEnglish
Pages (from-to)178-193
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
Publication statusPublished - 27 May 2013


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

    Research areas

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

ID: 57686331