The AT20G high frequency survey selects a very
high fraction of active galactic nuclei (AGNs) compared to surveys at lower
frequencies. The 6-km interferometer visibility using the 6 km antenna of the
ATCA can be used to obtain angular resolution information on sources (Y-axis
on the right). The catalogue of 6-km visibilities for AT20G sources published
as the AT20G
high-angular-resolution catalogue (Chhetri, Ekers, Jones and Ricci 2013).
The synergistic combination of the spectral index information for the sources
with the 6-km visibility gives the diagnostic plot above that can be used
to clearly identify different populations of radio sources. Notable are the
sources on the bottom right labelled "flat-spectrum extended sources".
Combining the radio data with infrared data from WISE a number of galactic and
extragalactic thermal sources (mostly planetary nebula) have been identified
(details published in Chhetri, Ekers, Kimball, Miszalski, Cohen and Manick 2015). The
remaining sources in this region may be either gravitational lenses or binary
black hole AGNs.