On the origin of radio core emission in radio-quiet quasars

We present a model for the radio emission from radio-quiet quasar nuclei. We show that a thermal origin for the high brightness temperature, flat spectrum point sources ( known as radio " cores") is possible provided that the emitting region is hot and optically thin. We hence demonstrate that optically thin bremsstrahlung from a slow, dense disk wind can make a significant contribution to the observed levels of radio core emission. This is a much more satisfactory explanation, particularly for sources where there is no evidence of a jet, than a sequence of self-absorbed synchrotron components that collectively conspire to give a flat spectrum. Furthermore, such core phenomena are already observed directly via milliarcsecond radio imaging of the Galactic microquasar SS 433 and the active galaxy NGC 1068. We contend that radio- emitting disk winds must be operating at some level in radio- loud quasars and radio galaxies as well ( although in these cases, observations of the radio cores are frequently contaminated/ dominated by synchrotron emission from jet knots). This interpretation of radio core emission mandates mass accretion rates that are substantially higher than Eddington. Moreover, acknowledgment of this mass- loss mechanism as an AGN feedback process has important implications for the input of energy and hot gas into the intergalactic medium ( IGM) since it is considerably less directional than that from jets.