Abstract
We utilize a series of galaxy formation simulations to investigate the
relationship between the ultraviolet (UV) slope, β, and the
infrared excess (IRX) in the spectral energy distributions (SEDs) of
galaxies. Our main goals are to understand the origin of and scatter in
the IRX-β relation; to assess the efficacy of simplified stellar
population synthesis screen models in capturing the essential physics in
the IRX-β relation; and to understand systematic deviations from
the canonical local IRX-β relations in particular populations of
high-redshift galaxies. Our main results follow. Young galaxies with
relatively cospatial UV and IR emitting regions and a Milky Way-like
extinction curve fall on or near the standard Meurer relation. This
behaviour is well captured by simplified screen models. Scatter in the
IRX-β relation is dominated by three major effects: (i) older
stellar populations drive galaxies below the relations defined for local
starbursts due to a reddening of their intrinsic UV SEDs; (ii) complex
geometries in high-z heavily star-forming galaxies drive galaxies
towards blue UV slopes owing to optically thin UV sightlines; (iii)
shallow extinction curves drive galaxies downwards in the IRX-β
plane due to lowered near-ultraviolet/far-ultraviolet extinction ratios.
We use these features of the UV slopes of galaxies to derive a fitting
relation that reasonably collapses the scatter back towards the
canonical local relation. Finally, we use these results to develop an
understanding for the location of two particularly enigmatic populations
of galaxies in the IRX-β plane: z ˜ 2-4 dusty star-forming
galaxies and z > 5 star-forming galaxies.
Original language | English |
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Pages (from-to) | 1718-1736 |
Journal | Monthly Notices of the Royal Astronomical Society |
Volume | 474 |
Issue number | 2 |
DOIs | |
Publication status | Published - 6 Nov 2017 |
Keywords
- dust
- extinction
- galaxies: high-redshift
- galaxies: ISM