Oral Presentation Astronomical Society of Australia Annual Scientific Meeting including HWWS 2013

The duty cycle of galaxy cluster AGN (#68)

Kevin Pimbblet 1 , Stanislav Shabala , Chris Haines , Amelia Fraser-McKelvie , David Floyd
  1. Monash University, Clayton, Vic, Australia

Mergers have frequently been cited as a method to fuel and feed the growth of AGN. Given that the fuel source for AGN is in the gas phase, any physical environmental mechanism that has the potential to disturb the morphology of a galaxy such as harassment may also produce an enhancement of AGN activity, not simply mergers.  But there exists a strong body of literature that also holds that environment plays little to no role in the incidence of AGN.  Here, we present an analysis of spectroscopically-identified optical AGN down to a cluster magnitude of M*+1 in a sample of 6 self-similar SDSS galaxy clusters at z=0.07. These clusters are specifically selected to lack significant substructure at bright limits in their central regions so that we are largely able to eliminate the local action of merging clusters on the frequency of AGN. We will detail how the AGN incidence varies with cluster position and in velocity phase-space as a function of mass, before turning to how AGN "retire" using the WHAN diagnostic to separate weak AGN from "retired galaxies", in which the main ionization mechanism comes from old stellar populations.  We demonstrate that cluster AGN have no special position inside galaxy clusters: they are neither preferentially located in the infall regions, nor situated at local maxima of galaxy density which is at apparent odds with results from X-ray analysis. Our results suggest that if interactions with other galaxies are responsible for triggering AGN activity, the time-lag between trigger and AGN enhancement must be sufficiently long to obfuscate the encounter site and wipe out the local galaxy density signal