Predicting the Number of Radio Sources Seen by Both VLASS and LSST

TL;DR

This paper predicts that the upcoming LSST optical survey will identify optical counterparts for approximately one million radio sources detected by VLASS, based on analysis of existing survey data and extrapolation.

Contribution

It introduces a method to estimate the number of VLASS radio sources that will have optical counterparts in LSST, using Hyper Suprime-Cam data for analysis.

Findings

LSST is expected to detect optical counterparts for about 1 million VLASS radio sources.

The analysis shows the fraction of radio sources with optical detections increases with optical brightness.

Extrapolation suggests a significant increase in multi-wavelength source identification in the next decade.

Abstract

Radio surveys typically sample extragalactic sources in higher redshift regimes than is typical for optical surveys, resulting in many radio sources not having a detected optical counterpart. Over the next decade the Legacy Survey of Space and Time (LSST) will be performing the deepest ($i < 26.4\,$mag) wide-area optical survey to date increasing the fraction of radio sources for which we have optical data. In this Research Note we use the Hyper Suprime-Cam survey to analyse how the fraction of radio sources in the Very Large Array Sky Survey (VLASS) with optical detections varies as a function of $i$-band magnitude and extrapolate to predict the number of optical counterparts we expect LSST to detect. Assuming a final VLASS point source depth of $S_{3\,\text{GHz}}\lesssim350\,\mu$Jy, we expect LSST to identify optical counterparts to $\sim 10^6$ radio sources in VLASS.