Deep ALMA photometry of distant X-ray AGN: improvements in star formation rate constraints, and AGN identification
Journal article, 2018

We present the star formation rates (SFRs) of a sample of 109 galaxies with
X-ray selected active galactic nuclei (AGN) with moderate to high X-ray luminosities (L(2-8keV) = 10^42 - 10^45 erg/s),
at redshifts 1 < z <4.7, that were selected to be faint or undetected in the Herschel bands.
We combine our deep ALMA continuum observations with deblended 8-500um photometry
from Spitzer and Herschel, and use infrared (IR) 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 F(870um)/F(24um)--redshift plane as
a tool for the identification of MIR emitting AGN, for three different samples representing AGN dominated, star formation dominated,
and composite sources. We demonstrate that the F(870um)/F(24um)--redshift plane can successfully split between AGN and star formation
dominated sources, and can be used as an AGN identification method.

galaxies: active

galaxies: evolution

galaxies: star formation


Flora Stanley

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics, Extragalactic Astrophysics

C. M. Harrison

European Southern Observatory (ESO)

D. M. Alexander

Durham University

J. Simpson

Academia Sinica

Kirsten Kraiberg Knudsen

Chalmers, Space, Earth and Environment, Astronomy and Plasmaphysics, Extragalactic Astrophysics

J. R. Mullaney

University of Sheffield

D. J. Rosario

Durham University

J. Scholtz

Durham University

Monthly Notices of the Royal Astronomical Society

0035-8711 (ISSN) 1365-2966 (eISSN)

Vol. 478 3 3721-3739

Subject Categories

Astronomy, Astrophysics and Cosmology


Basic sciences



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