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A remarkably flat relationship between the average star formation rate and AGN luminosity for distant X-ray AGN

Stanley, F.; Harrison, C.M.; Alexander, D.M.; Swinbank, A.M.; Aird, J.A.; Del Moro, A.; Hickox, R.C.; Mullaney, J.R.

A remarkably flat relationship between the average star formation rate and AGN luminosity for distant X-ray AGN Thumbnail


Authors

F. Stanley

C.M. Harrison

J.A. Aird

A. Del Moro

R.C. Hickox

J.R. Mullaney



Abstract

In this study, we investigate the relationship between the star formation rate (SFR) and AGN luminosity (LAGNLAGN) for ∼2000 X-ray detected AGN. The AGN span over three orders of magnitude in X-ray luminosity (1042<L2−8keV<1045.5ergs−11042<L2−8keV<1045.5ergs−1) and are in the redshift range z = 0.2–2.5. Using infrared (IR) photometry (8–500 μmμm), including deblended Spitzer and Herschel images and taking into account photometric upper limits, we decompose the IR spectral energy distributions into AGN and star formation components. Using the IR luminosities due to star formation, we investigate the average SFRs as a function of redshift and AGN luminosity. In agreement with previous studies, we find a strong evolution of the average SFR with redshift, tracking the observed evolution of the overall star-forming galaxy population. However, we find that the relationship between the average SFR and AGN luminosity is broadly flat at all redshifts and across all the AGN luminosities investigated; in comparison to previous studies, we find less scatter amongst the average SFRs across the wide range of AGN luminosities investigated. By comparing to empirical models, we argue that the observed flat relationship is due to short time-scale variations in AGN luminosity, driven by changes in the mass accretion rate, which wash out any underlying correlations between SFR and LAGNLAGN. Furthermore, we show that the exact form of the predicted relationship between SFR and AGN luminosity (and its normalization) is highly sensitive to the assumed intrinsic Eddington ratio distribution.

Journal Article Type Article
Acceptance Date Jul 22, 2015
Online Publication Date Aug 17, 2015
Publication Date Oct 11, 2015
Deposit Date Feb 9, 2016
Publicly Available Date Feb 12, 2016
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 453
Issue 1
Pages 591-604
DOI https://doi.org/10.1093/mnras/stv1678
Keywords Galaxies: active, Ggalaxies: evolution, Infrared: galaxies, X-rays: galaxies.
Public URL https://durham-repository.worktribe.com/output/1412760

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Copyright Statement
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.






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