# The XXL Survey XVIII. ATCA 2.1 GHz radio source catalogue and source counts for the XXL-South field

## TL;DR

This paper presents the largest 2.1 GHz radio source catalogue for the XXL-South field, including source counts and spectral index analysis, based on ATCA observations covering 25 square degrees.

## Contribution

It provides the first large-area, high-sensitivity 2.1 GHz radio survey of the XXL-South field with detailed source catalogues and counts, expanding the data available for extragalactic radio source studies.

## Key findings

- Catalogued 6287 radio sources with 26.4% resolved.
- Median spectral index of -0.75 for sources, consistent with AGN.
- Radio source counts agree with other surveys.

## Abstract

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.