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Cold dust emission from X-ray AGN in the SCUBA-2 Cosmology Legacy Survey : dependence on luminosity, obscuration and AGN activity.

Banerji, Manda and McMahon, R. G. and Willott, C. J. and Geach, J. E. and Harrison, C. M. and Alaghband-Zadeh, S. and Alexander, D. M. and Bourne, N. and Coppin, K. E. K. and Dunlop, J. S. and Farrah, D. and Jarvis, M. and Michałowski, M. J. and Page, M. and Smith, D. J. B. and Swinbank, A. M. and Symeonidis, M. and van der Werf, P. P. (2015) 'Cold dust emission from X-ray AGN in the SCUBA-2 Cosmology Legacy Survey : dependence on luminosity, obscuration and AGN activity.', Monthly notices of the Royal Astronomical Society., 454 (1). pp. 419-438.


We study the 850-μm emission in X-ray-selected active galactic nuclei (AGN) in the ∼2 deg2 COSMOS field using new data from the SCUBA-2 Cosmology Legacy Survey. We find 19 850-μm bright X-ray AGN in a ‘high-sensitivity’ region covering 0.89 deg2 with flux densities of S850 = 4–10 mJy. The 19 AGN span the full range in redshift and hard X-ray luminosity covered by the sample – 0.7 ≲ z ≲ 3.5 and 43.2 ≲ log10(LX) ≲ 45. We report a highly significant stacked 850-μm detection of a hard X-ray flux-limited population of 699 z > 1 X-ray AGN – S850 = 0.71 ± 0.08 mJy. We explore trends in the stacked 850-μm flux densities with redshift, finding no evolution in the average cold dust emission over the redshift range probed. For type 1 AGN, there is no significant correlation between the stacked 850-μm flux and hard X-ray luminosity. However, in type 2 AGN the stacked submillimeter flux is a factor of 2 higher at high luminosities. When averaging over all X-ray luminosities, no significant differences are found in the stacked submillimeter fluxes of type 1 and type 2 AGN as well as AGN separated on the basis of X-ray hardness ratios and optical-to-infrared colours. However, at log10(L2 − 10/erg s−1) > 44.4, dependences in average submillimeter flux on the optical-to-infrared colours become more pronounced. We argue that these high-luminosity AGN represent a transition from a secular to a merger-driven evolutionary phase where the star formation rates and accretion luminosities are more tightly coupled. Stacked AGN 850-μm fluxes are compared to the stacked fluxes of a mass-matched sample of K-band-selected non-AGN galaxies. We find that at 10.5 <log10(M*/M⊙)<11.5, the non-AGN 850-μm fluxes are 1.5–2 times higher than in type 2 AGN of equivalent mass. We suggest these differences are due to the presence of massive dusty, red starburst galaxies in the K-band-selected non-AGN sample, which are not present in optically selected catalogues covering a smaller area.

Item Type:Article
Keywords:Quasars: general, X-rays: galaxies, Galaxies: evolution, Submillimetre: galaxies.
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Publisher statement:This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2015 The Author Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Date accepted:12 August 2015
Date deposited:12 February 2016
Date of first online publication:22 September 2015
Date first made open access:No date available

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