Estimating black hole masses of blazars

TL;DR

This paper introduces a new method for estimating black hole masses in blazars, addressing contamination issues from jets, and applies it to well-known blazars to improve mass accuracy.

Contribution

It proposes a novel BLR size relation based on H-beta luminosity and combines it with host galaxy analysis for better black hole mass estimates in radio-loud AGNs.

Findings

New BLR size relation improves mass estimates for blazars.

Black hole masses for OJ 287, AO 0235+164, and 3C 66B are estimated using the proposed methods.

Implications for studies of blazar evolution and jet physics.

Abstract

Estimating black hole masses of blazars is still a big challenge. Because of the contamination of jets, using the previously suggested size -- continuum luminosity relation can overestimate the broad line region (BLR) size and black hole mass for radio-loud AGNs, including blazars. We propose a new relation between the BLR size and $H_{\beta}$ emission line luminosity and present evidences for using it to get more accurate black hole masses of radio-loud AGNs. For extremely radio-loud AGNs such as blazars with weak/absent emission lines, we suggest to use the fundamental plane relation of their elliptical host galaxies to estimate the central velocity dispersions and black hole masses, if their velocity dispersions are not known but the host galaxies can be mapped. The black hole masses of some well-known blazars, such as OJ 287, AO 0235+164 and 3C 66B, are obtained using these two methods and the M - $\sigma$ relation. The implications of their black hole masses on other related studies are also discussed.