The SOFIA Massive (SOMA) Radio Survey. II. Radio Emission from High-luminosity Protostars

We present centimeter continuum observations of seven high-luminosity massive protostars and their surrounding sources in regions with multiple targets, as part of the SOFIA Massive (SOMA) Star Formation Survey. With data from the Very Large Array and the Australia Telescope Compact Array, we analyze the spectral index, morphology, and multiplicity of the detected radio sources. The high-sensitivity, high-resolution observations allow us to resolve many sources; 65% of the reported sources are resolved at least within the synthesized beam. We report 15 new detections, 13 of which are entirely new, and 2 have counterparts at other wavelengths but are detected here for the first time at radio frequencies. We use the observations to build radio spectral energy distributions to calculate spectral indices. With radio morphologies and the spectral indices, we give assessments on the nature of the sources, highlighting six sources that display a radio jetlike morphology and a spectral index consistent with ionized jets. Combining with the SOMA Radio I sample, we present the radio–bolometric luminosity relation, especially probing the regime from Lbol ∼ 104 to 106L⊙. Here, we find a steep rise in radio luminosity, which is expected by models that transition from shock ionization to photoionization.