The stellar population in the SARAO MeerKAT Galactic Plane Survey

TL;DR

This study cross-matched MeerKAT radio sources with Gaia data to identify stellar counterparts, revealing a diverse population of radio-emitting stars in the Galactic plane, and highlighting the potential and limitations of current radio-optical matching methods.

Contribution

It presents the largest Galactic plane radio-optical crossmatch sample to date, combining two approaches to identify stellar counterparts to radio sources with detailed stellar classification.

Findings

629 potential stellar counterparts identified

Diverse stellar populations including OB stars, giants, YSOs, and white dwarfs

Active magnetically stars like RS CVn binaries and flare stars detected

Abstract

We report on optically selected stellar candidates of SARAO MeerKAT 1.3 GHz radio continuum survey sources of the Galactic plane. Stellar counterparts to radio sources are selected by cross-matching the MeerKAT source positions with \textit{Gaia} DR3, using two approaches. The first approach evaluated the probability of chance alignments between the radio survey and \textit{Gaia} sources and used AllWISE infrared colour-colour information to select potential stellar candidates. The second approach utilized a Monte Carlo method to evaluate the cross-matching reliability probability, based on populations of known radio-emitting stars. From the combined approaches, we found 629 potential stellar counterparts, of which 169 have existing SIMBAD classifications, making it the largest Galactic plane radio-optical crossmatch sample to date. A colour-magnitude analysis of the sample revealed a diverse population of stellar objects, ranging from massive OB stars, main-sequence stars, giants, young stellar objects, emission line stars, red dwarfs and white dwarfs. Some of the proposed optical counterparts include chromospherically/coronally active stars, for example RS CVn binaries, BY Dra systems, YSOs and flare stars, which typically exhibit radio emission. Based on Gaia's low-resolution spectroscopy, some of the stars show strong H$\alpha$ emission, indicating they are magnetically active, consistent with them being radio emitters. While MeerKAT's sensitivity and survey speed make it ideal for detecting faint radio sources, its angular resolution limits accurate counterpart identification for crowded fields such as the Galactic Plane. Higher frequency, and, thereby, better spatial resolution, radio observations plus circular polarization would be required to strengthen the associations.