Broad spectral lines in AGNs and supermassive black hole mass measurements

TL;DR

This paper reviews various spectral line-based methods for measuring supermassive black hole masses in AGNs, including a new polarization-based approach, highlighting the diversity of spectral diagnostics from X-ray to IR.

Contribution

It provides a comprehensive overview of existing spectral line methods and introduces a novel polarization technique for SMBH mass estimation in Type 1 AGNs.

Findings

Broad emission lines from X-ray to IR are used for SMBH mass estimates.

A new polarization-based method for SMBH mass measurement is proposed.

The review discusses the assumptions and limitations of virialization in line-based methods.

Abstract

The mass measurement of supermassive black holes (SMBHs) is a very complex task. Between several methods for SMBH mass measurements, some of them use the spectral lines, which indicate the motion of the emitting/absorbing material around an SMBH. Mostly there is assumption of virialization of line emitting gas in the region close to SMBHs that is used for their mass measurements. In this paper we will give an overview of methods for the SMBH mass measurements using broad emission spectral lines observed in Type 1 AGNs. First we give the basic idea to use the parameters of broad lines to SMBH mass measurements. After that we give an overview of broad lines from X-ray (Fe k{\alpha}) to the IR (Pashen and Brecket lines) which have been used for SMBH mass estimates. Additionally, we describe and discuss a new method for SMBH mass measurements using the polarization in the broad lines emitted from Type 1 AGNs.