A novel black-hole mass scaling relation based on coronal gas, and its dependence with the accretion disc

TL;DR

This paper introduces a new black hole mass scaling relation based on coronal gas line ratios, linking the ionising continuum to black hole mass and accretion disc temperature, supported by photoionisation models.

Contribution

It presents a novel BH-mass scaling relation using coronal line ratios and explores its dependence on accretion disc temperature through modeling.

Findings

A new BH-mass relation with 0.47 dex dispersion over $10^6$-$10^8$ M$_{igodot}$

The relation is driven by the effective temperature of the accretion disc

Photoionisation models support the temperature-mass anti-correlation

Abstract

Using bona-fide black hole (BH) mass estimates from reverberation mapping and the line ratio [SiVI] 1.963$\mu$m/Br$\gamma_{\rm broad}$ as tracer of the AGN ionising continuum, a novel BH-mass scaling relation of the form log($M_{\rm BH}) = (6.40\pm 0.17) - (1.99\pm 0.37) \times$ log ([SiVI]/Br$\gamma_{\rm broad})$, dispersion 0.47 dex, over the BH mass interval, $10^6 - 10^8$ M$_{\odot}$ is found. Following on the geometrically thin accretion disc approximation and after surveying a basic parameter space for coronal lines production, we believe one of main drivers of the relation is the effective temperature of the disc, which is effectively sampled by the [SiVI] 1.963$\mu$m coronal line for the range of BH masses considered. By means of CLOUDY photoionisation models, the observed anti-correlation appears to be formally in line with the thin disc prediction T_disc $\propto {M_{\rm BH}}^{-1/4}$.