The Role of MHD in the ICM and its Interactions with AGN Outflows

Magnetic fields probably play a central role in the dynamics and thermodynamics of ICMs and their interactions with AGNs, despite the fact that the fields usually contribute relatively little pressure; i.e., the ICM is a high-$\beta$'' plasma. More typically, the roles of magnetic fields come through microscopic’’ influences on charged particle behaviors, and through magnetic tension, which can still be significant in subsonic, high-$\beta$ flows. I briefly review these issues, while exploring the underlying question of using the commonly-applied magnetohydrodynamics model in the ICM when Coulomb scattering mean free paths can sometimes exceed tens of kiloparsecs.