Investigating the origin of radio emission in candidate super-Eddington accreting black holes

Abstract: Recent works show that the radio power of quasars accreting at very high rates can reach surprisingly high values. These studies suggest that this radio emission might originate from star formation, but lack of data leaves open the possibility that they could also contain a jetted active galactic nucleus (AGN). We investigate the origin of the radio emission of a sample of 18 super-Eddington candidates, over a wide range of redshifts. These sources are expected to have extreme radiative output per unit black hole mass, show high-velocity outflows and are therefore thought to be a prime mover of galactic evolution via radiative and mechanical feedback. We present new Karl G. Jansky Very Large Array (VLA) observations at L, C and X-band of these sources, which we combine with observations from the LOw-Frequency ARray (LOFAR) Two-metre Sky Survey (LoTSS) and the Very Large Array Sky Survey (VLASS). We also use optical and IR data to derive estimates of accretion and wind parameters, as well as star formation rates to compare with the ones derived from the radio emission. Based on the radio variability, luminosity, morphology, radio spectral properties, radio vs IR estimates of star formation rate and radio-to-mid IR flux ratio, we find that 7 of our 18 targets are likely to have their radio emission predominantly coming from SF, and 6 from a combination of SF and AGN-related mechanisms, while only three sources indicate a core or jetted AGN only origin for the detected radio emission. This is consistent with previous studies, and supports the prevalence of lower power radio structures associated with star-forming activity rather than relativistic jets in the high Eddington ratio regime. In the same sample, however, we find three sources for which the data suggest a concomitant presence of super-Eddington accretion and relativistic ejections.