Non-thermal radio emission from massive protostars in the SARAO MeerKAT Galactic Plane Survey

We present an investigation of the L-band emission from known massive young stellar objects in the South African Radio Astronomy Observatory MeerKAT Galactic Plane Survey to search for non-thermal radio emitters in the sample. A total of 398 massive protostars, identified from the Red MSX Source survey, are located within the survey region. Among these, 162 fields that host the protostars are isolated from nearby bright H ii regions, allowing for the study of any ionized jets present. Seventy-one of these fields have jets with five-sigma detections or higher, corresponding to a detection rate of 44 per cent. The MeerKAT fluxes of the detections, together with the upper limits of the non-detections and any other fluxes from previous observations, were used to estimate the spectral indices of the jets, and to search for the presence of non-thermal radiation. In cases where a source manifests as single in a given observation but is resolved into multiple components in observations of higher resolutions, the sum of the fluxes of the resolved components was used in estimating the indices. Any effects from missing flux in higher resolution observations were incorporated into the index uncertainties. The spectral indices of the sample show that at least 50 per cent of the jets emit non-thermal radiation. Additionally, the spectral energy distribution of some of the sources, as well as their radio luminosities exhibit evidence of non-thermal emission, especially in extended sources.