An Outflow from the X-Ray Corona as the Origin of Millimeter Emission from Radio-quiet AGNs

Abstract Recent observations of radio-quiet active galactic nuclei have shown the presence of millimeter emission, whose origin remains unknown, from within parsec scales of the central black hole. We argue that the millimeter 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 millimeter emission. In this model, the 100 GHz emission originates from within ≲10 4 gravitational radii ( r g ) of the central black hole, though the projected distance from the black hole can be as low as 50 r g depending on the line of sight. Our model predicts a flat emission spectrum <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>F</mml:mi> <mml:mi>ν</mml:mi> </mml:msub> <mml:mo>∼</mml:mo> <mml:mi>const</mml:mi> </mml:math> and a millimeter-to-X-ray luminosity ratio L mm / L X ∼ 10 −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 magnetohydrodynamic 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 millimeter-emitting regions.