The SARAO MeerKAT 1.3 GHz Galactic Plane Survey: Compact Source Catalogue

We present a catalogue of compact sources detected in the SARAO MeerKAT 1.3 GHz Galactic Plane Survey (SMGPS). We extract 471 681 compact sources from the survey maps covering the regions 252° < l < 358° and 2° < l < 61° at |b| < 1.5°, which have an angular resolution of 8ⁿ and a sensitivity of ∼ 10-30 µJy beam−1. Here we describe the source identification and characterisation methods, present the quality assurance of the catalogue, explore the nature of the catalogue sources, and present initial science highlights. We define compact sources to be those with less than five 8′′ beam areas. The catalogue is highly reliable and is ∼97% complete for sources with a signal-to-noise ratio ≥ 5, and has a false positive rate of less than 1%. We therefore limit our catalogue to sources with a signal-to-noise ratio ≥ 5. We find that the bulk of the catalogue sources are unknown. Only ∼1% are associated with previously known sources and are predominantly high-flux density sources: ∼90% of the sources with Sν > 1 Jy and ∼65% with Sν > 100 mJy are previously known. Thus, the majority of the unknown population are at sub-mJy levels. We have detected radio continuum emission associated with 385 radio quiet WISE HII region candidates that were undetected in previous radio continuum studies. We show images that compare the SMGPS compact sources to CORNISH ultracompact (UC) HII regions, thus highlighting the sensitivity and unprecedented uv-coverage of the SMGPS. Finally, we look at the association of methanol maser emission with radio continuum emission by comparison with the methanol multibeam (MMB) survey. We find that 15% of the maser population in the MMB survey is coincident (< 4′′ separation) with radio continuum emission, in agreement with previous studies. This shows that methanol maser emission and radio continuum emission are rarely detected together, and implies that we are more likely to see methanol masers around young HII regions than more evolved HII regions.