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

TL;DR

This paper proposes a model where millimeter emission in radio-quiet AGN originates from an extended, magnetically connected outflow near the X-ray corona, explaining observed spectra and luminosity ratios.

Contribution

It introduces an analytic model linking mm emission to the X-ray corona via a magnetized outflow, supported by GRMHD simulations, providing new insights into AGN emission mechanisms.

Findings

The mm emission originates within ~10^4 gravitational radii of the black hole.

The model predicts a flat spectrum and a mm-to-X-ray luminosity ratio of about 10^-4.

The results are consistent with observational data.

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.