paper

The IRX- relation: Insights from simulations

arXiv:1604.07402 · doi:10.3847/1538-4357/aa6c5b

Abstract

We study the relationship between the UV continuum slope and infrared excess (IRX) predicted by performing dust radiative transfer on a suite of hydrodynamical simulations of galaxies. Our suite includes both isolated disk galaxies and mergers intended to be representative of galaxies at both and . Our low-redshift isolated disks and mergers often populate a region around the the locally calibrated \citet[][M99]{M99} relation but move well above the relation during merger-induced starbursts. Our high-redshift simulated galaxies are blue and IR-luminous, which makes them lie above the M99 relation. The value of UV continuum slope strongly depends on the dust type used in the radiative transfer calculations: Milky Way-type dust leads to significantly more negative (bluer) slopes compared with Small Magellanic Cloud-type dust. The effect on due to variations in the dust composition with galaxy properties or redshift can dominate over other sources of variations and is the dominant model uncertainty. The dispersion in is anticorrelated with specific star formation rate and tends to be higher for the simulations. In the actively star-forming simulated galaxies, dust attenuation dominates the dispersion in , whereas in the simulations, the contributions of SFH variations and dust are similar. For low-SSFR systems at both redshifts, SFH variations dominate the dispersion. Finally, the simulated isolated disks and mergers both occupy a region in the \irxbeta\ plane consistent with observed dusty star-forming galaxies (DSFGs). Thus, contrary to some claims in the literature, the blue colors of high-z DSFGs do not imply that they are short-lived starbursts.

20 pages+a 4-page appendix, Accepted for publication at ApJ

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