Polarization in broad emission lines of Active Galactic Nuclei

TL;DR

This paper reviews how polarization measurements of broad emission lines in type 1 AGNs reveal the geometry of the broad line region and help estimate supermassive black hole masses.

Contribution

It provides a comprehensive overview of recent theoretical and observational studies on polarization in broad lines of AGNs, highlighting methods to infer BLR structure and SMBH mass.

Findings

Polarization depends on BLR geometry and scattering mechanisms.

Polarization angle profiles can estimate SMBH mass.

Recent investigations enhance understanding of AGN structure.

Abstract

We discuss the polarization of broad emission lines in the type 1 active galactic nuclei (AGNs). The polarization depends on the geometry of the broad line region (BLR), and also on the polarization mechanism, or distribution of the scattering material. Therefore the polarization measurements can indicate the geometry of the BLR and the mechanism of polarization (equatorial or polar scattering). In addition, the polarization angle (PA) shape across the line profile can be used to measure the supermassive black hole (SMBH) mass, and constrain the BLR characteristics. We give an overview of ours and other recent investigations of the polarization in broad lines from both aspects: theoretical and observational.