June 2016


How important is the gas mass for triggering AGN activity?

In the previous plot of the month I showed that AGN can be triggered by galaxy mergers. But what about the gas reservoir? Shouldn’t it also be important?
The plot above shows the mean gas mass of the progenitor galaxies (i.e. before the merger) versus redshift. The three different panels show inactive galaxies, low luminosity AGN, and high luminosity AGN. Blue and red/yellow lines correspond to two different simulations from the Magneticum Pathfinder simulation set, which cover different mass ranges. The different symbols/colours show galaxies with major mergers, minor mergers, and without mergers. For redshifts below z=2 the gas masses are in general higher for low luminosity AGN than for inactive galaxies, but only for the simulation containing more massive galaxies (blue lines). For high luminosity AGN this trend is only visible for non-merging galaxies.
This means that at below z=2 the gas mass is a driving factor for triggering low luminosity AGN independently of the merger history, as well as high luminosity AGN in galaxies without mergers. At z=2 the gas mass is no driving factor for triggering AGN activity.