Close supermassive binary black holes

TL;DR

This paper questions the interpretation of blueshifted emission lines in AGNs as evidence of supermassive black hole binaries, proposing instead a disc emission explanation and discussing implications for SMB merger timescales.

Contribution

It challenges the binary black hole interpretation of certain AGN emission lines and suggests alternative disc emission explanations, impacting SMB merger theories.

Findings

No clear optical spectral evidence for close SMBs in the studied AGN.

Alternative disc emission model can explain the observed spectral features.

Implications for SMB merger timescales and accretion processes.

Abstract

It has been proposed that when the peaks of the broad emission lines in active galactic nuclei (AGNs) are significantly blueshifted or redshifted from the systemic velocity of the host galaxy, this could be a consequence of orbital motion of a supermassive blackhole binary (SMB) (Gaskell 1983). The AGN J1536+0441 (=SDSS J153636.22+044127.0) has recently been proposed as an example of this phenomenon (Boroson & Lauer 2009). It is proposed here instead that 1536+044 is an example of line emission from a disc. If this is correct, the lack of clear optical spectral evidence for close SMBs is significant and argues either that the merging of close SMBs is much faster than has generally been hitherto thought, or if the approach is slow, that when the separation of the binary is comparable to the size of the torus and broad-line region, the feeding of the black holes is disrupted.