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The use of ultraviolet (UV) emission as a tracer of galaxy star formation rate (SFR) is hampered by dust obscuration. The empirical relationship between UV-slope, β, and the ratio between far-infrared and UV luminosity, IRX, is commonly employed to account for obscured UV emission. We present a simple model that explores the physical origin of variations in the IRX–β dust attenuation relation. A relative increase in FUV compared to NUV attenuation and an increasing stellar population age cause variations towards red UV-slopes for a fixed IRX. Dust geometry effects (turbulence, dust screen with holes, mixing of stars within the dust screen, two-component dust model) cause variations towards blue UV-slopes. Poor photometric sampling of the UV spectrum causes additional observational variations. We provide an analytic approximation for the IRX–β relation invoking a subset of the explored physical processes (dust type, stellar population age, turbulence). We discuss observed variations in the IRX–β relation for local (sub-galactic scales) and high-redshift (normal and dusty star-forming galaxies, galaxies during the epoch of reionization) galaxies in the context of the physical processes explored in our model. High spatial resolution imaging of the UV and sub-mm emission of galaxies can constrain the IRX–β dust attenuation relation for different galaxy types at different epochs, where different processes causing variations may dominate. These constraints will allow the use of the IRX–β relation to estimate intrinsic SFRs of galaxies, despite the lack of a universal relation.
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Popping et al. (2017) studied this question.
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