Abstract
Using deep Herschel and ALMA observations, we investigate the star formation
rate (SFR) distributions of X-ray AGN host galaxies at 0.5<z<1.5 and 1.5<z<4,
comparing them to that of normal, star-forming (i.e., "main-sequence", or MS)
galaxies. We find 34-55 per cent of AGNs have SFRs at least a factor of two
below that of the average MS galaxy, compared to ~15 per cent of all MS
galaxies, suggesting significantly different SFR distributions. Indeed, when
both are modelled as log-normal distributions, the mass and redshift-normalised
SFR distributions of AGNs are roughly twice as broad, and peak ~0.4 dex lower,
than that of MS galaxies. However, like MS galaxies, the normalised SFR
distribution of AGNs appears not to evolve with redshift. Despite AGNs and MS
galaxies having different SFR distributions, the linear-mean SFR of AGNs
derived from our distributions is remarkably consistent with that of MS
galaxies, and thus with previous results derived from stacked Herschel data.
This apparent contradiction is due to the linear-mean SFR being biased by
bright outliers, and thus does not necessarily represent a true
characterisation of the typical SFR of AGNs.
Description
[1506.05459] ALMA and Herschel reveal that AGN and main-sequence galaxies have different star formation rate distributions
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