The XXL Survey XVIII. ATCA 2.1 GHz radio source catalogue and source
  counts for the XXL-South field
  The 2.1 GHz radio source catalogue of the 25 deg$^2$ ultimate XMM
extragalactic survey south (XXL-S) field, observed with the Australia Telescope
Compact Array (ATCA), is presented. The final radio mosaic achieved a
resolution of $\sim$$4.8"$ and a median rms noise of $\sigma \approx41$
$\mu$Jy/beam. To date, this is the largest area radio survey to reach this flux
density level. A total of 6350 radio components above 5$\sigma$ are included in
the component catalogue, 26.4% of which are resolved. Of these components, 111
were merged together to create 48 multiple-component radio sources, resulting
in a total of 6287 radio sources in the source catalogue, 25.9% of which were
resolved. A survival analysis revealed that the median spectral index of the
Sydney University Molonglo Sky Survey (SUMSS) 843 MHz sources in the field is
$\alpha$ = $-$0.75, consistent with the values of $-0.7$ to $-0.8$ commonly
used to characterise radio spectral energy distributions of active galactic
nuclei (AGN). The 2.1 GHz and 1.4 GHz differential radio source counts are
presented and compared to other 1.4 GHz radio surveys. The XXL-S source counts
show good agreement with the other surveys.
