The Millimeter/X-ray Relation in Rapidly Accreting Supermassive Black Holes at z <0.16

TL;DR

This study extends the known millimeter/X-ray correlation in AGN to higher luminosities and redshifts, revealing deviations likely due to different coronal electron populations and additional emission mechanisms.

Contribution

It provides new observational evidence for the mm/X-ray relation in more luminous, higher-redshift AGN and proposes a two-component coronal model to explain deviations.

Findings

High-luminosity AGN lie above the established mm/X-ray correlation.

A second-degree polynomial best fits the combined sample with 0.32 dex scatter.

mm emission correlates linearly with UV disk luminosity and bolometric luminosity.

Abstract

A tight correlation between nuclear millimeter (mm) and X-ray emission has recently been found in nearby ($z < 0.01$) and low-Eddington ratio ($\rm \lambda_{Edd} < 0.1$) radio-quiet (RQ) Active Galactic Nuclei (AGN), suggesting a common origin in the hot X-ray corona. We test this relation in nine more distant RQ AGN ($z \sim 0.06-0.16$) with higher bolometric luminosities ($\log(L_{\rm bol}/\mathrm{erg\,s^{-1}})=45.3-46.3$), Eddington ratios ($\rm \lambda_{Edd} = 0.19-0.85$), and X-ray bolometric corrections ($\kappa_{2-10}=29-194$), selected from the Burst Alert Telescope (BAT) survey. We obtained quasi-simultaneous observations with Swift at 2-10 keV and the Atacama Large Millimeter/submillimeter Array (ALMA) at 100 GHz and with high angular resolution ($<0.14$"). We find that these high-luminosity AGN lie above the mm/X-ray correlation defined by lower-luminosity sources. A joint fit to both samples yields a second-degree polynomial with an intrinsic scatter of 0.32 dex. Furthermore, the mm emission correlates linearly with both the UV disk luminosity and $L_{\rm bol}$, with intrinsic scatters of 0.45 and 0.35 dex, respectively. We propose that the deviation from the linear mm/X-ray relation arises from a two-component coronal electron population: thermal electrons that produce X-rays, but become less efficient at higher luminosities, and non-thermal electrons that produce mm emission and remain tied to $L_{\rm bol}$. Additional mm emission from outflow-driven shocks may also contribute, though SED modeling and spectral index studies favor a coronal origin.