Comment on the Black Hole Recoil Candidate Quasar SDSS J092712.65+294344.0

TL;DR

This paper analyzes the spectral features of quasar SDSS J092712.65+294344.0, exploring whether it is a recoiling black hole, a binary system, or a superposition of two AGN, using new observations and spectral analysis.

Contribution

It provides new spectroscopic observations and analysis that challenge the recoiling black hole hypothesis, favoring the superposition of two AGN scenario.

Findings

Confirmation of spectral features with Hobby-Eberly Telescope

Detection of a third redshift system at 900 km/s

Constraints on black hole recoil and binary models

Abstract

SDSS J092712.65+294344.0 has been proposed as a candidate for a supermassive black hole (~10^8.8 solar masses) ejected at high speed from the host galactic nucleus by gravitational radiation recoil, or alternatively for a supermassive black hole binary. This is based on a blueshift of 2650 km/s of the broad emission lines ("b-system") relative to the narrow emission lines ("r-system") presumed to reflect the galaxy velocity. New observations with the Hobby-Eberly Telescope (HET) confirm the essential features of the spectrum. We note a third redshift system, characterized by weak, narrow emission lines of [O III] and [O II] at an intermediate velocity 900 km/s redward of the broad line velocity ("i-system"). A composite spectrum of SDSS QSOs similar to J0927 illustrates the feasibility of detecting the calcium K absorption line in spectra of sufficient quality. The i-system may represent the QSO host galaxy or a companion. Photoionization requires the black hole to be ~3 kpc from the r-system emitting gas, implying that we are observing the system only 10^6 yr after the recoil event and contributing to the low probability of observing such a system. The HET observations give an upper limit of 10 km/s per year on the rate of change of the velocity difference between the r- and b-systems, constraining the orbital phase in the binary model. These considerations and the presence of a cluster of galaxies apparently containing J0927 favor the idea that this system represents a superposition of two AGN.