On the H i content, dust-to-gas ratio and nature of Mg II absorbers

Brice Ménard, Doron Chelouche

Research output: Contribution to journalArticlepeer-review


We estimate the mean dust-to-gas ratio of Mg ii absorbers as a function of rest equivalent width W0 and redshift over the range 0.5 < z < 1.4. Using the expanded Sloan Digital Sky Survey/Hubble Space Telescope sample of low-redshift Lyman-α absorbers, we first show the existence of a 8σ correlation between the mean hydrogen column density 〈N H i〉 and W0, an indicator of gas velocity dispersion. By combining these results with recent dust-reddening measurements, we show that the mean dust-to-gas ratio of Mg ii absorbers does not appreciably depend on rest equivalent width. Assuming that, on average, dust-to-gas ratio is proportional to metallicity, we find its redshift evolution to be consistent with that of L* galaxies from z = 0.5 to 1.4, and we show that our constraints disfavour dwarf galaxies as the origin of such absorbers. We discuss other scenarios and favour galactic outflows from ∼L * galaxies as the origin of the majority of strong Mg ii absorbers. Finally, we show that, once evolutionary effects are taken into account, the Bohlin et al. relation between AV and NH is also satisfied by strong Mg ii systems down to lower column densities than those probed in our Galaxy.

Original languageEnglish
Pages (from-to)808-815
Number of pages8
JournalMonthly Notices of the Royal Astronomical Society
Issue number3
StatePublished - Mar 2009
Externally publishedYes


  • Galaxies: haloes
  • ISM: dust, extinction
  • Quasars: absorption lines

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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