The Invisible AGN Catalogue: A Mid-Infrared - Radio Selection Method for
  Optically-Faint Active Galactic Nuclei
  A large fraction of active galactic nuclei (AGN) are "invisible" in extant
optical surveys due to either distance or dust-obscuration. The existence of
this large population of dust-obscured, infrared-bright AGN is predicted by
models of galaxy - supermassive black hole coevolution and is required to
explain the observed X-ray and infrared backgrounds. Recently, infrared
colour-cuts with WISE have identified a portion of this missing population.
However, as the host galaxy brightness relative to that of the AGN increases,
it becomes increasingly difficult to differentiate between infrared emission
originating from the AGN and from its host galaxy. As a solution, we have
developed a new method to select obscured AGN using their 20 cm continuum
emission to identify the objects as AGN. We created the resulting Invisible AGN
Catalogue by selecting objects that are detected in AllWISE (mid-IR) and FIRST
(20 cm), but are not detected in SDSS (optical) or 2MASS (near-IR), producing a
final catalogue of 46,258 objects. 30 per cent of the objects are selected by
existing selection methods, while the remaining 70 per cent represent a
potential previously-unidentified population of candidate AGN that are missed
by mid-infrared colour cuts. Additionally, by relying on a radio continuum
detection, this technique is efficient at detecting radio-loud AGN at z > 0.29,
regardless of their level of dust obscuration or their host galaxy's relative
brightness.
