Comparison between the influence of outflows and supermassive binary black holes in active galactic nuclei on the polarization angle profiles

TL;DR

This study investigates how the polarization angle profiles in active galactic nuclei differ between models with supermassive binary black holes and single black holes, suggesting spectropolarimetry as a tool to detect binary systems.

Contribution

The paper introduces a comparative analysis of polarization profiles for SMBBHs and single SMBHs, highlighting distinctive symmetry features that can aid in identifying binary black holes.

Findings

SMBBHs produce axis-symmetric polarization angle profiles.

Single SMBHs generate point-symmetric polarization angle profiles.

Spectropolarimetry can distinguish between SMBH and SMBBH systems.

Abstract

Optical polarization signal coming from the innermost part of active galactic nuclei (AGNs) is highly sensitive on the geometry and kinematics of the central engine. Due to the compact size of the AGN central region, which is spatially unresolved with current observing facilities, we rely on spectropolarimetry which can provide us insight in their hidden physics. We model equatorial scattering for various broad line region (BLR) configurations using radiative transfer code STOKES. We analyze the polarization position angle () profiles for four supermassive binary black holes (SMBBHs) models and compare them with the profiles found for a unified model in AGNs with a single supermassive black hole (SMBH) and with notable outflowing velocity component of the BLR.. We find that the profiles for SMBBHs are axis-symmetric, while the profiles for a single SMBHs are point-symmetric and that there is a clear distinction between the two cases. Our conclussion is that spectropolarimetry might play a key role in the search for the SMBBHs by inspecting the polarization angle profiles.