Submillimetre observations of WISE/radio-selected AGN and their environments

Abstract

We present JCMT SCUBA-2 850 μm submillimetre (submm) observations of 30 mid-infrared (mid-IR) luminous active galactic nuclei (AGNs), detected jointly by the Wide-field Infrared Survey Explorer (WISE) all-sky IR survey and the NVSS/FIRST radio survey. These rare sources are selected by their extremely red mid-IR spectral energy distributions (SEDs) and compact radio counterparts. Further investigations show that they are highly obscured, have abundant warm AGN-heated dust and are thought to be experiencing intense AGN feedback. These galaxies appear to be consistent with a later AGN-dominated phase of merging galaxies, while hot, dust-obscured galaxies are an earlier starburst-dominated phase. When comparing the number of submm galaxies detected serendipitously in the surrounding 1.5 arcmin to those in blank-field submm surveys, there is a very significant overdensity, of order 5, but no sign of radial clustering centred at our primary objects. The WISE/radio-selected AGN thus reside in 10-Mpc-scale overdense environments that could be forming in pre-viralized clusters of galaxies. WISE/radio-selected AGNs appear to be the strongest signposts of high-density regions of active, luminous and dusty galaxies. SCUBA-2 850 μm observations indicate that their submm fluxes are low compared to many popular AGN SED templates, hence the WISE/radio-selected AGNs have either less cold and/or more warm dust emission than normally assumed for typical AGN. Most of the targets are not detected, only four targets are detected at SCUBA-2 850 μm, and have total IR luminosities ≥1013 L{bull's eye}, if their redshifts are consistent with the subset of the 10 SCUBA-2 undetected targets with known redshifts, z ~ 0.44-2.86.