A Universal Relation of Dust Obscuration Across Cosmic Time

Jianbo Qin, Xian Zhong Zheng, Stijn Wuyts, Zhizheng Pan, Jian Ren

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We investigate dust obscuration as parametrized by the infrared excess IRX ≡ L IR/L UV in relation to global galaxy properties, using a sample of ∼32 000 local star-forming galaxies (SFGs) selected from SDSS (Sloan Digital Sky Survey), GALEX (Galaxy Evolution Explorer), and WISE (Wide-field Infrared Survey Explorer). We show that IRX generally correlates with stellar mass (M ), star formation rate, gas-phase metallicity (Z), infrared luminosity (L IR), and the half-light radius (R e). A weak correlation of IRX with axial ratio (b/a) is driven by the inclination and thus seen as a projection effect. By examining the tightness and the scatter of these correlations, we find that SFGs obey an empirical relation of the form IRX = 10 α (L IR) β R e −γ (b/a) −δ, where the power-law indices all increase with metallicity. The best-fitting relation yields a scatter of ∼0.17 dex and no dependence on stellar mass. Moreover, this empirical relation also holds for distant SFGs out to z = 3 in a population-averaged sense, suggesting it to be universal over cosmic time. Our findings reveal that IRX approximately increases with L IR/R e [1.3−1.5] instead of L IR/R e 2 (i.e. surface density). We speculate this may be due to differences in the spatial extent of stars versus star formation and/or complex star-dust geometries. We conclude that not stellar mass but IR luminosity, metallicity, and galaxy size are the key parameters jointly determining dust obscuration in SFGs.

Original languageEnglish
Pages (from-to)5733-5751
Number of pages19
JournalMonthly Notices of the Royal Astronomical Society
Issue number4
Publication statusPublished - 15 Mar 2019


  • Dust
  • Extinction
  • Galaxies: ISM
  • Galaxies: evolution
  • Galaxies: star formation
  • Galaxies: statistics

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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