Morphology of X-ray AGN hosts

A sizeable fraction (~30%) of X-ray selected AGN at z<1 is asociated with spiral galaxy hosts. This argues against major mergers as the only mechanism for triggering accretion events onto supermassive black holes.

The top figure is a gallery of the Hubble Space Telescope optical morphologies of moderate luminosity X-ray selected at z<1. They show diverse morphologies, inlcuding disk, bulge-dominated early-type hosts and morphologically disturbed systems. If major galaxy mergers are responsible for triggering black hole accretion, one expects AGN to live in hosts with disturbed/irregular morphology or bulges, i.e. the end product of major mergers. The fact that AGN are observed in disk galaxies suggests that processes other than major mergers also play a role in the growth of black holes. More details in Georgakakis et al. 2009.