A Universal Relation of Dust Obscuration Across Cosmic Time. (arXiv:1903.05121v1 [astro-ph.GA])

A Universal Relation of Dust Obscuration Across Cosmic Time. (arXiv:1903.05121v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Qin_J/0/1/0/all/0/1">Jianbo Qin</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Zheng_X/0/1/0/all/0/1">X. Z. Zheng</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Wuyts_S/0/1/0/all/0/1">Stijn Wuyts</a> (2), <a href="http://arxiv.org/find/astro-ph/1/au:+Pan_Z/0/1/0/all/0/1">Zhizheng Pan</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Ren_J/0/1/0/all/0/1">Jian Ren</a> (1) ((1) Purple Mountain Observatory, CAS, (2) University of Bath)

We investigate dust obscuration as parameterised by the infrared excess
IRX$equiv$$L_{rm IR}/L_{rm UV}$ in relation to global galaxy properties,
using a sample of $sim$32$,$000 local star-forming galaxies (SFGs) selected
from SDSS, GALEX and WISE. We show that IRX generally correlates with stellar
mass ($M_ast$), star formation rate (SFR), gas-phase metallicity ($Z$),
infrared luminosity ($L_{rm IR}$) and the half-light radius ($R_{rm 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 $IRX$=$10^alpha,(L_{rm
IR})^{beta},R_{rm e}^{-gamma},(b/a)^{-delta}$ where the power-law indices
all increase with metallicity. The best-fitting relation yields a scatter of
$sim$0.17$,$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 $L_{rm IR}/R_{rm e}^{[1.3 – 1.5]}$ instead
of $L_{rm IR}/R_{rm e}^{2}$ (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.

We investigate dust obscuration as parameterised by the infrared excess
IRX$equiv$$L_{rm IR}/L_{rm UV}$ in relation to global galaxy properties,
using a sample of $sim$32$,$000 local star-forming galaxies (SFGs) selected
from SDSS, GALEX and WISE. We show that IRX generally correlates with stellar
mass ($M_ast$), star formation rate (SFR), gas-phase metallicity ($Z$),
infrared luminosity ($L_{rm IR}$) and the half-light radius ($R_{rm 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 $IRX$=$10^alpha,(L_{rm
IR})^{beta},R_{rm e}^{-gamma},(b/a)^{-delta}$ where the power-law indices
all increase with metallicity. The best-fitting relation yields a scatter of
$sim$0.17$,$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 $L_{rm IR}/R_{rm e}^{[1.3 – 1.5]}$ instead
of $L_{rm IR}/R_{rm e}^{2}$ (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.

http://arxiv.org/icons/sfx.gif

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