A novel black hole mass scaling using coronal lines in active galaxies

TL;DR

This paper introduces a new black hole mass scaling relation based on coronal line ratios in active galaxies, providing a simpler alternative to traditional methods with comparable accuracy.

Contribution

The study presents a novel BH-mass scaling relation using the [Si VI]/Brγ ratio, applicable to single-epoch spectra, reducing observational effort compared to existing techniques.

Findings

Derived a BH-mass relation with 0.47 dex dispersion.

Sample includes 21 Type-1 AGNs within 10^6-10^8 M_sun.

Offers an efficient alternative for BH mass estimation.

Abstract

Using bonafide black hole (BH) mass estimates from reverberation mapping and the line ratio [Si VI]1.963$\mu$m/Br$\gamma_{\rm broad}$ as tracer of the Active Galactic Nuclei (AGN) ionizing continuum, we find 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 ([Si VI]/Br$\gamma_{\rm broad})$, over the BH mass interval, $10^6 - 10^8$ M$_{\odot}$. The current sample consists of 21 Type-1 AGNs with the overall dispersion in our scaling relation at 0.47 dex, one that emulates the well-established M-$\sigma$ relation which shows a dispersion $\sim$0.44 dex. The new scaling offers an economic, and physically motivated alternative for BH estimate using single epoch spectra, avoiding large telescope time (reverberation mapping) or absolute flux calibration (the continuum luminosity method). With the advent of big surveys in the infrared in the near future, we aim to reduce the scatter in the relation by supplementing with more sources.