What Triggers Active Galaxies? (Plus, an Unexpected Find)

Active galaxies (AGN), whose central black holes are actively pulling in gas and radiating light from the core, cover a wide range of luminosities and types of host galaxies. What triggers this behavior, turning a normal galaxy active? It is often assumed that galaxy mergers are responsible for the most powerful AGN, like quasars, while the weaker examples have some other cause. This can be tested by looking at the shapes of the host galaxies to seek signs of mergers. I will show the results of our Hubble imaging campaign, as well as an unexpected (and so far unexplained) find in one field.