A Quick Look at the $3$GHz Radio Sky I. Source Statistics from the Very Large Array Sky Survey

Abstract

The Very Large Array Sky Survey (VLASS) is observing the entire sky north of $-40^{\circ }$ in the S-band ($2<\hat{I}½<4$GHz), with the highest angular resolution ($2^{\prime \prime }.5$) of any all-sky radio continuum survey to date. VLASS will cover its entire footprint over three distinct epochs, the first of which has now been observed in full. Based on Quick Look images from this first epoch, we have created a catalog of $1.9\times 10^6$ reliably detected radio components. Due to the limitations of the Quick Look images, component flux densities are underestimated by $\sim 15\%$ at $S_{\text{peak}}>3$mJy/beam and are often unreliable for fainter components. We use this catalog to perform statistical analyses of the $\hat{I}½\sim 3$GHz radio sky. Comparisons with the Faint Images of the Radio Sky at Twenty cm survey (FIRST) show the typical $1.4-3$GHz spectral index, $\hat{I}\pm$, to be $\sim -0.71$. The radio color-color distribution of point and extended components is explored by matching with FIRST and the LOFAR Two Meter Sky Survey. We present the VLASS source counts, $dN/dS$, which are found to be consistent with previous observations at $1.4$ and $3$GHz. Resolution improvements over FIRST result in excess power in the VLASS two-point correlation function at angular scales $\lesssim 7^{\prime \prime }$, and in $18\%$ of active galactic nuclei associated with a single FIRST component being split into multi-component sources by VLASS.

Accepted for publication in ApJS; 23 pages, 18 figures, 4 tables. Revised version includes new flux calibration (section 3.2) that results in VLASS fluxes being scaled by 15% in the presented analyses rather than the 10% used in the earlier version. Associated VLASS catalog data available at https://cirada.ca/catalogues