VLA FRAMEx. III. Circumnuclear Radio Emission Mechanisms in Hard X-Ray Selected Active Galactic Nuclei

Abstract We present Stokes I continuum analysis for a volume-limited sample (<40 Mpc) of hard X-ray selected active galactic nuclei (AGNs) using 4–12 GHz observations with the Karl G. Jansky Very Large Array (VLA). All 25 sources analyzed here have previously been observed with the Very Long Baseline Array (VLBA) to probe their subparsec projected physical scales, but detected emission has only been measured for 12 of the sources at the C band (4.4 GHz), despite expectations. We determined that coronal emission is unlikely to be a dominant emission mechanism for the sources not detected by the VLBA, and the emission measured with the VLA is likely produced beyond parsec spatial scales. We also explore potential radiation mechanisms for the circumnuclear radio emission that is produced beyond the observable parsec physical scales probed with the VLBA but within the ≤30–110 pc spatial scales observed with the VLA. From an energetics perspective, we find that all targets have extranuclear radio emission that is compatible with AGN winds, assuming a maximum of 10% of the bolometric output can supply the mechanical energy observed. We also find that the excess emission is likely too strong for star formation alone when compared to results from optical spectroscopy, but may contribute in smaller capacities.