April 2016


How many galaxies appear as AGN?

This plot shows the mean number of AGN, depending on the total halo mass at different redshifts. Interestingly, this figure looks completely different for central AGN (bottom panel) than for satellite AGN (top panel). While the number of AGN in substructures continuously increases, the evolution of the number of central AGN is more complex: at low redshifts, it decreases very strongly in a group environment and increases again in galaxy clusters. We suspect that AGN feedback suppresses AGN activity in galaxy groups, while the black holes in galaxy clusters are so massive that gravity dominates. In contrast, at high redshifts, where the gas fractions are much larger, almost all galaxies contain a central AGN.

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