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ALMA and Herschel reveal that X-ray-selected AGN and main-sequence galaxies have different star formation rate distributions

Lookup NU author(s): Dr Christopher HarrisonORCiD


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© 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Using deep Herschel and ALMA observations, we investigate the star formation rate (SFR) distributions of X-ray-selected active galactic nucleus (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 that 34-55A per cent of AGNs in our sample have SFRs at least a factor of 2 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 lognormal distributions, the mass and redshift-normalized SFR distributions of X-ray AGNs are roughly twice as broad, and peak ≈0.4 dex lower, than that of MS galaxies. However, like MS galaxies, the normalized SFR distribution of AGNs in our sample appears not to evolve with redshift. Despite X-ray 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 characterization of the typical SFR of X-ray AGNs.

Publication metadata

Author(s): Mullaney JR, Alexander DM, Aird J, Bernhard E, Daddi E, Del Moro A, Dickinson M, Elbaz D, Harrison CM, Juneau S, Liu D, Pannella M, Rosario D, Santini P, Sargent M, Schreiber C, Simpson J, Stanley F

Publication type: Article

Publication status: Published

Journal: Monthly Notices of the Royal Astronomical Society: Letters

Year: 2015

Volume: 453

Issue: 1

Pages: L83-L87

Print publication date: 11/10/2015

Online publication date: 25/08/2015

Acceptance date: 29/07/2015

ISSN (print): 1745-3925

ISSN (electronic): 1745-3933

Publisher: Oxford University Press


DOI: 10.1093/mnrasl/slv110


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