A Universal Relation of Dust Obscuration Across Cosmic Time

Jianbo Qin; X. Z. Zheng; Stijn Wuyts; Zhizheng Pan; Jian Ren

doi:10.1093/mnras/stz763

paper

A Universal Relation of Dust Obscuration Across Cosmic Time

arXiv:1903.05121 · doi:10.1093/mnras/stz763

Abstract

We investigate dust obscuration as parameterised by the infrared excess IRX $\equiv$ $L_{IR} / L_{UV}$ in relation to global galaxy properties, using a sample of $\sim$ 32000 local star-forming galaxies (SFGs) selected from SDSS, GALEX and WISE. We show that IRX generally correlates with stellar mass ( $M_{*}$ ), star formation rate (SFR), 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 $I R X$ = $1 0^{α} (L_{IR})^{β} R_{e}^{- γ} (b / a)^{- δ}$ where the power-law indices all increase with metallicity. The best-fitting relation yields a scatter of $\sim$ 0.17dex 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.

22 pages, 14 figures, accepted for publication in the MNRAS

A Universal Relation of Dust Obscuration Across Cosmic Time

Abstract

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