Near-IR observations of the HE0450-2958 system: discovery of a second AGN?

TL;DR

This study uses near- and mid-infrared observations to reveal a hidden, reddened AGN in the companion galaxy of the QSO HE0450-2958, suggesting complex interactions and possible black hole ejection scenarios.

Contribution

It provides the first infrared detection of a likely obscured AGN in the companion galaxy, offering new insights into the system's complex dynamics and black hole interactions.

Findings

Discovery of a hidden, infrared-bright AGN in the companion galaxy.

Evidence supporting the presence of a heavily reddened, obscured AGN.

Discussion of a possible black hole ejection from the galaxy collision.

Abstract

The QSO HE0450-2958 was brought to the front scene by the non-detection of its host galaxy and strong upper limits on the latter's luminosity. The QSO is also a powerful infrared emitter, in gravitational interaction with a strongly distorted UltraLuminous InfraRed companion galaxy. We investigate the properties of the companion galaxy, through new near- and mid-infrared observations of the system obtained with NICMOS onboard HST, ISAAC and VISIR on the ESO VLT. The companion galaxy is found to harbour a point source revealed only in the infrared, in what appears as a hole or dark patch in the optical images. Various hypotheses on the nature of this point source are analyzed and it is found that the only plausible one is that it is a strongly reddened AGN hidden behind a thick dust cloud. The hypothesis that the QSO supermassive black hole might have been ejected from the companion galaxy in the course of a galactic collision involving 3-body black holes interaction is also reviewed, on the basis of this new insight on a definitely complex system.