The Metallicity Dependence of the HI Shielding Layers in Nearby Galaxies

Andreas Schruba, Shmuel Bialy, Amiel Sternberg

Research output: Contribution to journalArticlepeer-review


We investigate the metallicity dependence of H i surface densities in star-forming regions along many lines of sight within 70 nearby galaxies, probing kiloparsec to 50 pc scales. We employ H i, SFR, stellar mass, and metallicity (gradient) measurements from the literature, spanning a wide range (5 dex) in stellar and gas mass and (1.6 dex) in metallicity. We consider metallicities as observed, or rescaled to match the mass-metallicity relation determined for SDSS galaxies. At intermediate to high metallicities (0.3-2 times solar), we find that the H i surface densities saturate at sufficiently large total gas surface density. The maximal H i columns vary approximately inversely with metallicity, and show little variation with spatial resolution, galactocentric radius, or among galaxies. In the central parts of massive spiral galaxies, the H i gas is depressed by factors of ∼ 2. The observed behavior is naturally reproduced by metallicity dependent shielding theories for the H i-to-H2 transitions in star-forming galaxies. We show that the inverse scaling of the maximal H i columns with metallicity suggests that the area filling fraction of atomic-molecular complexes in galaxies is of the order of unity, and weakly dependent on metallicity.

Original languageEnglish
Article number110
JournalAstrophysical Journal
Issue number2
StatePublished - 1 Aug 2018


  • ISM: atoms
  • ISM: molecules
  • galaxies: ISM
  • radio lines: galaxies

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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