Submillimetre observations of X-ray active galactic nuclei in the William Herschel Deep Field

Abstract

We investigate the contribution made by active galactic nuclei (AGN) to the high-redshift, luminous, submillimetre (submm) source population using deep (≤2 mJy beam−1) Large Apex Bolometer Camera (LABOCA) 870 Graphicm observations within the William Herschel Deep Field. These submm data complement previously obtained Chandra X-ray data of the field, from which AGN have been identified with the aid of follow-up optical spectra. From the LABOCA data, we detect 11 submm sources (based on a detection threshold of 3.2σ) with estimated fluxes of ≳3 mJy beam−1. Of the 11 identified submm sources, we find that two coincide with observed AGN and that, based on their hardness ratios, both of these AGN appear to be heavily obscured. We perform a stacking of the submm data around the AGN, which we group by estimated NH column density, and find that only the obscured (NH > 1022 cm−2) AGN show significant associated submm emission. These observations support the previous findings of Page et al. and Hill & Shanks that obscured AGN preferentially show submm emission. Hill & Shanks have argued that, in this case, the contribution to the observed submm emission (and thus the submm background) from AGN heating of the dust in these sources may be higher than previously thought.