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

Recent observations of radio-quiet active galactic nuclei (RQAGN) have shown the presence of millimeter emission from within parsec scales of the central black hole, whose origin remains unknown. We argue that the mm emission comes from a spatially extended region that is connected to the compact X-ray corona via magnetic fields. We present an analytic model scaled to corona values in which electrons from multiple heights along an extended conical outflow shape the mm emission. We demonstrate this model's plausibility using a general relativistic magneto-hydrodynamic (GRMHD) simulation of a thin accretion disc as a case study. We find that the 100 GHz emission originates from within <10⁴ 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_ν∼const and a mm-to-X-ray luminosity ratio L_mm/L_X∼10^-4, consistent with observations. These quantities depend weakly on the underlying electron distribution function and black hole mass. Our model highlights the need to study continual dissipation along the outflow to connect the X-ray- and mm-emitting regions.