The effect of nuclear gas distribution on the mass determination of supermassive black holes

TL;DR

This paper investigates how the distribution of nuclear gas affects supermassive black hole mass estimates, proposing correction factors to improve accuracy and reduce uncertainties in understanding black hole and galaxy evolution.

Contribution

It introduces a correction factor for virial mass estimates based on gas distribution and line width, enhancing the precision of black hole mass measurements.

Findings

Correction factor inversely proportional to emission line width

Line-of-sight inclination explains observed effects

Radiation pressure can also account for the findings

Abstract

Supermassive black holes reside in the nuclei of most galaxies. Accurately determining their mass is key to understand how the population evolves over time and how the black holes relate to their host galaxies. Beyond the local universe, the mass is commonly estimated assuming virialized motion of gas in the close vicinity to the active black holes, traced through broad emission lines. However, this procedure has uncertainties associated with the unknown distribution of the gas clouds. Here we show that the comparison of black hole masses derived from the properties of the central accretion disc with the virial mass estimate provides a correcting factor, for the virial mass estimations, that is inversely proportional to the observed width of the broad emission lines. Our results suggest that line-of-sight inclination of gas in a planar distribution can account for this effect. However, radiation pressure effects on the distribution of gas can also reproduce our findings. Regardless of the physical origin, our findings contribute to mitigate the uncertainties in current black hole mass estimations and, in turn, will help to further understand the evolution of distant supermassive black holes and their host galaxies.