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Echoes, Explosions, and Enrichment: The Impact of AGN on the Cluster Environment

The realization that black holes with masses 10^6–10^9 M⊙ inhabit the nuclei of essentially all massive galaxies has been one of the most transformative advances in astrophysics of the past decade. It now seems likely that supermassive black holes play a central role in galaxy formation through a feedback process that regulates both star formation in the host galaxy and the rate of accretion onto the black hole itself. The high-pressure atmospheres of galaxy clusters serve as repositories for the mechanical energy released by AGN outbursts and by extension a historical record of this feedback process over time. This record routinely takes the form of observed cavity structures and shock fronts in the surrounding ICM and provides reliable constraints on AGN energetics. Despite their remarkably high power, however, it is clear that AGN are heating large volumes of gas in a gentle manner, such that cooling gas near the AGN continues to fuel modest amounts of star formation as well as the AGN itself. Similarly, recent work indicates that AGN outbursts are an important part of the elemental enrichment cycle in the ICM. In this talk I will present some examples of these recent results as well as discuss a number of the outstanding questions that remain with the feedback picture. Finally, I will discuss how the combination of X-ray data and new low-frequency radio samples will allow us to address some of these open questions as well as determine the impact of AGN feedback on the large-scale properties of clusters over cosmic time.