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Deep ALMA photometry of distant X-ray AGN: improvements in star formation rate constraints, and AGN identification

Stanley, F; Harrison, CM; Alexander, DM; Simpson, J; Knudsen, KK; Mullaney, J R; Rosario, DJ; Scholtz, J

Deep ALMA photometry of distant X-ray AGN: improvements in star formation rate constraints, and AGN identification Thumbnail


Authors

F Stanley

CM Harrison

J Simpson

KK Knudsen

J R Mullaney

DJ Rosario

J Scholtz



Abstract

We present the star formation rates (SFRs) of a sample of 109 galaxies with X-rayselected active galactic nuclei (AGNs) with moderate to high X-ray luminosities (L2−8 keV = 1042 − 1045 erg s−1), at redshifts 1 < z < 4.7, that were selected to be faint or undetected in the Herschel bands. We combine our deep Atacama large (sub-)millimetre array (ALMA) continuum observations with deblended 8–500 μm photometry from Spitzer and Herschel, and use infrared (IR) spectral energy distribution (SED) fitting and AGN – star formation decomposition methods. The addition of the ALMA photometry results in an order of magnitude more X-ray AGN in our sample with a measured SFR (now 37 %). The remaining 63 % of the sources have SFR upper limits that are typically a factor of 2–10 times lower than the pre-ALMA constraints. With the improved constraints on the IR SEDs, we can now identify a mid-IR (MIR) AGN component in 50 % of our sample, compared to only ∼1 % previously. We further explore the F870 μm/F24 μm–redshift plane as a tool for the identification of MIR-emitting AGN, for three different samples representing AGN-dominated, star formationdominated, and composite sources. We demonstrate that the F870 μm/F24 μm–redshift plane can successfully split between AGN and star formation-dominated sources, and can be used as an AGN identification method.

Citation

Stanley, F., Harrison, C., Alexander, D., Simpson, J., Knudsen, K., Mullaney, J., …Scholtz, J. (2018). Deep ALMA photometry of distant X-ray AGN: improvements in star formation rate constraints, and AGN identification. Monthly Notices of the Royal Astronomical Society, 478(3), 3721-3739. https://doi.org/10.1093/mnras/sty1044

Journal Article Type Article
Acceptance Date Apr 23, 2018
Online Publication Date May 7, 2018
Publication Date Aug 21, 2018
Deposit Date Sep 5, 2018
Publicly Available Date Sep 18, 2018
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 478
Issue 3
Pages 3721-3739
DOI https://doi.org/10.1093/mnras/sty1044
Public URL https://durham-repository.worktribe.com/output/1315777

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Copyright Statement
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society © 2018 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.






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