The nature of kinematically offset AGN

In a recent paper, Comerford & Greene (2014) presented a sample of SDSS AGN that are kinematically offset from their host galaxies. They suggest that these systems are supermassive black hole (SMBH) binaries, resulting from a recent merger, in which one of the SMBHs is accreting material but the other is not.

Two of their sample of 351 galaxies have already been observed by SAMI. One of them (in a group in GAMA) has a rotating gas disc but is a slow rotator in terms of its stellar kinematics. The different kinematics of the gas and stellar components may be a signature of a recent merger. The second AGN (in a cluster) shows simple disc rotation in both the gas and the stars, consistent between the two. In this case the "offset" AGN appears to be due to an outflow.

Crucially, in each case the gas velocity varies smoothly across the galaxy, whereas an SMBH binary would produce a discontinuity in the centre. Therefore these AGN are unlikely to be in binary systems.

This paper will be short and quick. We will discuss the kinematics of the two galaxies and describe the most likely explanations for the observed offsets. The main conclusions are:

1 - Offset AGN will by definition have unusual kinematic features, but those observed so far are unlikely to be SMBH binaries.

2 - IFU observations are required to understand offset AGN - single-fibre observations do not give the necessary information.

Publication Date: 
November 2014