New insights on the recoiling/binary black hole candidate J0927+2943 via molecular gas observations

TL;DR

This study uses molecular gas observations and optical imaging to investigate the peculiar QSO J0927+2943, ruling out recoiling or binary black hole scenarios and a superposition of galaxies, but leaving the origin of certain emission lines unresolved.

Contribution

The paper provides new molecular gas and optical data that challenge previous black hole motion hypotheses for J0927+2943, narrowing down possible explanations.

Findings

Galactic-scale molecular gas at the same redshift as the QSO broad lines

Recoiling/binary black hole scenarios are ruled out

Superposition model is disfavored but less constrained

Abstract

The peculiar QSO J0927+2943 shows multiple sets of emission lines in its optical spectrum. This signature has been interpreted as the relative motion between a black hole, either recoiling or bound in a binary system, and its host galaxy, or as a superposition of two galaxies along the line of sight. In order to test these scenarios, we have collected 2mm CO(2-1) observations using the IRAM Plateau de Bure Interferometer, and optical images and spectroscopy at the Calar Alto observatory. Together with archival HST images, these data provide unique insights on the nature of this system. The recoiling/binary black hole scenarios are ruled out by the clear detection of a galactic-scale molecular gas reservoir at the same redshift of the QSO broad lines. The observations presented here also disfavour the superposition model, although with less constraints. Thus, the origin of the second, bright set of narrow emission lines in J0927+2943 is still unknown.