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

Mullaney, J.R. and Alexander, D.M. and Aird, J. and Bernhard, E. and Daddi, E. and Del Moro, A. and Dickinson, M. and Elbaz, D. and Harrison, C.M. and Juneau, S. and Liu, D. and Pannella, M. and Rosario, D. and Santini, P. and Sargent, M. and Schreiber, C. and Simpson, J. and Stanley, F. (2015) 'ALMA and Herschel reveal that X-ray-selected AGN and main-sequence galaxies have different star formation rate distributions.', Monthly notices of the Royal Astronomical Society : letters., 453 (1). L83-L87.


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 34–55 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.

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Publisher statement:This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society: Letters ©: 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:29 July 2015
Date deposited:15 June 2016
Date of first online publication:25 August 2015
Date first made open access:No date available

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