MeerKAT discovery of 164 compact radio rings towards the Galactic plane

ABSTRACT We report the discovery of 164 compact (radius < 1 arcmin) radio rings using MeerKAT 1.3 GHz data from the SARAO (South African Radio Astronomy Observatory) MeerKAT Galactic Plane Survey ($l=2^{\circ } \!-\! 60^{\circ }, 252^{\circ } \!-\! 358^{\circ }$, $|b|\le 1.5^{\circ }$) and the Galactic Centre mosaic, from a search aimed at identifying previously uncatalogued radio sources. Within this sample, approximately 19 per cent of the rings contain a central point radio source. A multiwavelength analysis reveals a striking diversity: about 40 per cent of the rings enclose an isolated infrared point source, 50 per cent exhibit an extended counterpart in the mid- or far-infrared, and several are only detected in the radio band. We found that 17 per cent of the rings in the sample are positionally coincident (within 5 arcsec) with known entries in SIMBAD, including unclassified infrared sources, spiral galaxies, young stellar objects, and long-period variable candidates. Based on these matches and exploiting ancillary multiwavelength data and catalogues, we explore several formation scenarios for the rings, such as H ii regions, planetary nebulae, mass-loss relics from evolved massive stars, supernova remnants, nova shells, galaxies, galaxy cluster lenses, and odd radio circles. Tentative classifications are proposed for nearly 60 per cent of the sample. These results highlight the potential of MeerKAT to uncover previously undetected compact radio structures and, particularly, recover missing Galactic radio-emitting objects.