2010ApJ...708..462H

One of the legacies of the Chandra era is the discovery of active galactic nucleus (AGN) inflated X-ray cavities in virtually all cool-core clusters, with mechanical luminosities comparable to or larger than the cluster cooling rate, suggesting that AGN might be responsible for heating clusters. This discovery poses a new set of questions that cannot be addressed by X-ray imaging or modeling alone: are AGNs actually responsible for halting cooling flows? How is the AGN energy transferred to heat? How tight is the observed balance between heating and cooling? One of the critical unanswered questions currently posed is the actual expansion velocity of these cavities, which cannot be measured from imaging alone. This uncertainty propagates into the calculation of the jet power required to inflate the cavities and affects all arguments of feedback power. Using numerical simulations of jet-driven cavities in fully dynamically evolved clusters and a new virtual X-ray observatory tool, we demonstrate that high-resolution, high-throughput X-ray spectroscopy will be able to answer this question and that the International X-ray Observatory will have the necessary capabilities to deliver the necessary measurements. We also discuss the evolution of the turbulent velocity distribution of the cluster in response to the action of radio galaxies and how it might be used as a probe in studying feedback.