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Durham University

Department of Physics

Staff profile

Publication details for Prof David Alexander

Banerji, Manda, McMahon, R. G., Willott, C. J., Geach, J. E., Harrison, C. M., Alaghband-Zadeh, S., Alexander, D. M., Bourne, N., Coppin, K. E. K., Dunlop, J. S., Farrah, D., Jarvis, M., Michałowski, M. J., Page, M., Smith, D. J. B., Swinbank, A. M., Symeonidis, M. & 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): 419-438.

Author(s) from Durham


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