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

Abstract

Using bona-fide black hole (BH) mass estimates from reverberation mapping and the line ratio [Si VI] 1.963$\rm{\mu m}$/Brγ_broad as tracer of the AGN ionizing continuum, a novel BH-mass scaling relation of the form log(M_BH) = (6.40 ± 0.17) - (1.99 ± 0.37) × log ([Si VI]/Brγ_broad), dispersion 0.47 dex, over the BH mass interval, 10⁶-10⁸ M_⊙ 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 [Si VI] 1.963$\rm{\mu m}$ coronal line for the range of BH masses considered. By means of CLOUDY photoionization models, the observed anticorrelation appears to be formally in line with the thin disc prediction T_disc ∝ M_BH^-1/4.