From the accretion disk to the cluster halo: the multi-scale physics of black hole feedback

It is firmly established that supermassive black holes (SMBHs) have a profound influence on the evolution of galaxies and galaxy groups/clusters. Yet, almost 20 years after this realization, fundamental questions remain. What determines the efficiency with which an active galactic nucleus (AGN) couples to its surroundings? Why does AGN feedback appear to be ineffective in low-mass galaxies? In maintenance-mode feedback, how does the AGN regulate to closely balance cooling? How does the nature of AGN feedback change as we consider higher redshifts and push back to the epoch of the first galaxies? AGN feedback is a truly multi-scale phenomenon. Observations show that AGN have an energetic impact on galactic-, group-, and cluster-halo scales. Yet the efficiency with which an accreting SMBH releases energy, and the partitioning of that energy into radiation, winds, and relativistic jets, is dictated by complex processes in the accretion disk on AU scales, 10^10 times smaller than the halo. Furthermore, especially in massive systems where feedback proceeds via the heating of a hot circumgalactic or intracluster medium (CGM/ICM), the relevant microphysics of the hot baryons is unclear, requiring an understanding of plasma instabilities on 10^-9pc scales. We propose a set of projects that explore the multiscale physics of AGN feedback. Magnetohydrodynamic models of accretion disks will be constructed to study the AGN radiation/winds/jets and calibrate observable proxies of SMBH mass and accretion rate. We will use the machinery of plasma physics to characterize the CGM/ICM microphysics relevant to the thermalization of AGN-injected energy. Finally, we will produce new galaxy-, group- and cluster-scale models incorporating the new microphysical prescriptions and AGN models. Our new theoretical understanding of AGN feedback as a function of halo mass, environment, and cosmic time is essential for interpreting the torrent of data from current and future observatories