An outflow from the X-ray corona as the origin of millimeter emission from radio-quiet AGN

Abstract

Recent observations of radio-quiet active galactic nuclei (RQAGN) have shown the presence of millimeter emission, whose origin remains unknown, from within parsec scales of the central black hole. We argue that the mm emission comes from a spatially extended region that is magnetically connected to the compact X-ray corona, in analogy to the solar wind and corona. We present an analytic model scaled to corona values in which non-equipartition electrons from multiple heights along an extended conical outflow shape the mm emission. In this model, the 100 GHz emission originates from within $\lesssim10^4$ gravitational radii ($r_g$) of the central black hole, though the projected distance from the black hole can be as low as $50r_g$ depending on the line-of-sight. Our model predicts a flat emission spectrum $F_{\nu}\sim{\rm const}$ and a mm-to-X-ray luminosity ratio $L_{\rm mm}/L_X\sim10^{-4}$, consistent with observations. These quantities depend weakly on the underlying electron power-law distribution function and black hole mass. We demonstrate this model's plausibility using a general relativistic magneto-hydrodynamic (GRMHD) simulation of a thin accretion disc as a case study. Our model highlights the need to study continual dissipation along the outflow to connect the X-ray- and mm-emitting regions.