November 2016


What is the role of multiple mergers for triggering AGN activity?

This plot shows the fraction of AGN (different colours indicate different luminosity thresholds) in galaxies with major mergers (solid line) and minor mergers (dashed lines). In the plot of the month from May 2016 we have already seen that the fraction of AGN is higher in galaxy mergers than in non-merging galaxies. Now we distinguish between multiple and single mergers by counting all mergers within the last 1.5Gyr. The left panel includes only multiple mergers and the right panel shows the result for single mergers. In general we see that the AGN fraction is higher for multiple mergers than for single mergers for both minor and major mergers. Thus, the probability to find an AGN in a multiple merger is indeed higher than in a single merger. However, I would like to remark that the fraction of multiple mergers is relatively low (about 10-15% of all mergers) and thus, they play only a minor role for the total AGN population.