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A binning-free method reveals a continuous relationship between galaxies' AGN power and offset from main sequence

Lookup NU author(s): Dr Christopher HarrisonORCiD


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© 2020 The Author(s). Studies investigating the relationship between active galactic nucleus (AGN) power and the star formation rates (SFRs) of their host galaxies often rely on averaging techniques - such as stacking - to incorporate information from non-detections. However, averages, and especially means, can be strongly affected by outliers and can therefore give a misleading indication of the 'typical' case. Recently, a number of studies have taken a step further by binning their sample in terms of AGN power (approximated by the 2-10 keV luminosity of the AGN), and investigating how the SFR distribution differs between these bins. These bin thresholds are often weakly motivated, and binning implicitly assumes that sources within the same bin have similar (or even identical) properties. In this paper, we investigate whether the distribution of host SFRs - relative to the locus of the star-forming main sequence (i.e. RMS) - changes continuously as a function of AGN power. We achieve this by using a hierarchical Bayesian model that completely removes the need to bin in AGN power. In doing so, we find strong evidence that the RMS distribution changes with 2-10 keV X-ray luminosity. The results suggest that higher X-ray luminosity AGNs have a tighter physical connection to the star-forming process than lower X-ray luminosity AGNs, at least within the 0.8 < z < 1.2 redshift range considered here.

Publication metadata

Author(s): Grimmett LP, Mullaney JR, Bernhard EP, Harrison CM, Alexander DM, Stanley F, Masoura VA, Walters K

Publication type: Article

Publication status: Published

Journal: Monthly Notices of the Royal Astronomical Society

Year: 2020

Volume: 495

Issue: 1

Pages: 1392-1402

Print publication date: 01/06/2020

Online publication date: 16/05/2020

Acceptance date: 01/05/2020

ISSN (print): 0035-8711

ISSN (electronic): 1365-2966

Publisher: Oxford University Press


DOI: 10.1093/MNRAS/STAA1255


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