The Quasar SDSS J153636.22+044127.0: A Double-Peaked Emitter in a Candidate Binary Black-Hole System

TL;DR

This paper investigates the quasar SDSS J153636.22+044127.0, proposing it as a binary supermassive black hole system with double-peaked emission lines, and suggests such systems may be common among double-peaked emitters.

Contribution

It introduces a model combining a Keplerian disk and a binary SMBH system to explain peculiar emission lines, highlighting the potential prevalence of such binaries in AGNs.

Findings

Decomposition of emission lines supports the binary SMBH hypothesis.

Blue peaks originate from the secondary black hole's region.

Tidal interactions may create gaps and extended emission regions in the disk.

Abstract

Double-peaked emission lines are believed to be originated from accretion disks around supermassive black holes (SMBHs), and about 3% of z<0.33 AGNs are found to be double-peaked emitters. The quasar SDSS J153636.22+044127.0 has recently been identified with peculiar broad-line emission systems exhibiting multiple redshifts. We decompose the H$\alpha$ and H$\beta$ profiles into a circular Keplerian disk line component and other Gaussian components. We propose that the system is both a double-peaked emitter and a binary SMBH system, where the extra-flux in the blue peaks of the broad lines comes from the region around the secondary black hole. We suggest that such black hole binary systems might also exist in many known double-peaked emitters, where the tidal torques from the secondary black hole clear the outer region of the disk around the primary black hole, similar to the gap in a protostellar disk due to the process of planetary migration, and might also stimulate the formation of a vertical extended source in the inner region around the primary which illuminates the disk. However, most secondary SMBHs in such systems might be too small to maintain a detectable broad line region (BLR), so that the disk line from the primary dominates.