Emission Signatures from Sub-parsec Binary Supermassive Black Holes II: Effect of Accretion Disk Wind on Broad Emission Lines

TL;DR

This paper introduces an improved semi-analytic model for broad emission-line signatures from sub-parsec supermassive black hole binaries, accounting for accretion disk winds, and demonstrates its effectiveness in distinguishing binary systems.

Contribution

The study advances previous models by incorporating radiation-driven disk winds, enhancing the interpretation of emission-line profiles for supermassive black hole binaries.

Findings

Profile shapes better indicate binary separation and disk alignment.

Modeled profiles align more with observed SBHB candidates than with regular AGNs.

Genuine SBHBs likely include equal-mass, misaligned mini-disks.

Abstract

We present an improved semi-analytic model for calculation of the broad optical emission-line signatures from sub-parsec supermassive black hole binaries (SBHBs) in circumbinary disks. The second-generation model improves upon the treatment of radiative transfer by taking into account the effect of the radiation driven accretion disk wind on the properties of the emission-line profiles. Analysis of 42.5 million modeled emission-line profiles shows that correlations between the profile properties and SBHB parameters identified in the first-generation model are preserved, indicating that their diagnostic power is not diminished. The profile shapes are a more sensitive measure of the binary orbital separation and the degree of alignment of the black hole mini-disks, and are less sensitive to the SBHB mass ratio and orbital eccentricity. We also find that modeled profile shapes are more compatible with the observed sample of SBHB candidates than with our control sample of regular AGNs. Furthermore, if the observed sample of SBHBs is made up of genuine binaries, it must include compact systems with comparable masses, and misaligned mini-disks. We note that the model described in this paper can be used to interpret the observed emission-line profiles once a sample of confirmed SBHBs is available but cannot be used to prove that the observed SBHB candidates are true binaries.