An Ultra-deep Multi-band VLA Survey of the Faint Radio Sky (COSMOS-XS): Source Catalog and Number Counts

Abstract

We present ultra-deep, matched-resolution Karl G. Jansky Very Large Array (VLA) observations at 10 and $3$ GHz in the COSMOS field: the COSMOS-XS survey. The final 10 and $3$ GHz images cover $\sim 16{\mathrm{arcmin}}^2$ and $\sim 180{\mathrm{arcmin}}^2$ and reach median rms values of $0.41\hat{I}¼{\mathrm{Jy}\mathrm{beam}}^{-1}$ and $0.53\hat{I}¼{\mathrm{Jy}\mathrm{beam}}^{-1}$, respectively. Both images have an angular resolution of $\sim 2.0^{\prime \prime }$. To fully account for the spectral shape and resolution variations across the broad bands, we image all data with a multi-scale, multi-frequency synthesis algorithm. We present source catalogs for the 10 and $3$ GHz image with 91 and 1498 sources, respectively, above a peak brightness threshold of $5\ddot{I}ƒ$. We present source counts with completeness corrections included that are computed via Monte Carlo simulations. Our corrected radio counts at $3$ GHz with direct detections down to $\sim 2.8\hat{I}¼$Jy are consistent within the uncertainties with other results at 3 and 1.4 GHz, but extend to fainter flux densities than previous direct detections. The ultra-faint $3$ GHz number counts are found to exceed the counts predicted by the semi-empirical radio sky simulations developed in the framework of the SKA Simulated Skies project, consistent with previous P(D) analyses. Our measured source counts suggest a steeper luminosity function evolution for these faint star-forming sources. The semi-empirical Tiered Radio Extragalactic Continuum Simulation (T-RECS) predicts this steeper evolution and is in better agreement with our results. The $10$ GHz radio number counts also agree with the counts predicted by the T-RECS simulation within the expected variations from cosmic variance. In summary, the multi-band, matched-resolution COSMOS-XS survey in the well-studied COSMOS field provides a high-resolution view of the ultra-faint radio sky that can help guide next generation radio facilities.

Resubmitted to ApJ after incorporating suggestions from the referee; 20 pages, 17 figures. This is a companion paper to Algera et al., on arXiv today