The broad emission line asymmetry in low mass ratio of supermassive binary black holes on elliptical orbits

TL;DR

This paper models the broad emission line profiles from a supermassive binary black hole system with elliptical orbits and low mass ratio, revealing asymmetric, shifting lines that vary periodically with the orbit.

Contribution

It introduces a model for broad line profiles in low mass ratio SMBBHs with elliptical orbits, considering one active component with a BLR and the other inactive, and analyzes their spectral variability.

Findings

Broad line profiles are asymmetric and shifted.

Line profiles vary periodically with orbital motion.

Detected periodicity in line and continuum light curves.

Abstract

We investigate the broad line profiles emitted from a system supermassive binary black hole (SMBBH) having elliptical orbits and low mass ratio of $m_2/m_1\sim 0.1$. Our model assumes a super Eddington accretion flow in the case of a smaller component, whereas the massive component has very small or negligible accretion, therefore supposing that no broad line region (BLR) is attached to it. Thus, the proposed SMBBH system contains one moving BLR, associated with the less massive component and one circum-binary BLR. We study the effect of different total mass of the system (ranging from 10$^6$ to 10$^8$ Solar masses) to the $\mathrm{H\beta}$ line profiles and to the continuum and line light curves. The resulted broad line profiles are asymmetric and shifted, and are varying during the orbital period. The asymmetry in the broad line profiles is discussed in terms of expected differences between the proposed model of the SMBBH with one active component and the scenario of a recoiling black hole. We discuss the periodicity detected in the line and continuum light curves, as well as in the variations of the line asymmetry and shift.