The Impact of Radio AGN Bubble Composition on the Dynamics and Thermal Balance of the Intracluster Medium

Abstract

Feeding and feedback of active galactic nuclei (AGNs) are critical for understanding the dynamics and thermodynamics of the intracluster medium (ICM) within the cores of galaxy clusters. Although radio bubbles inflated by AGN jets could be dynamically supported by cosmic rays (CRs), the impact of CR-dominated jets is not well understood. In this work, we perform three-dimensional simulations of CR-jet feedback in an isolated cluster atmosphere; we find that CR jets impact the multiphase gas differently than jets dominated by kinetic energy. In particular, CR bubbles can more efficiently uplift the cluster gas and cause an outward expansion of the hot ICM. Due to adiabatic cooling from the expansion and less efficient heating from CR bubbles by direct mixing, the ICM is more prone to local thermal instabilities, which will later enhance chaotic cold accretion onto the AGN. The amount of cold gas formed during the bubble formation and its late-time evolution sensitively depend on whether or not CR transport processes are included. We also find that low-level, subsonic driving of turbulence by AGN jets holds for both kinetic and CR jets; nevertheless, the kinematics is consistent with the Hitomi measurements. Finally, we carefully discuss the key observable signatures of each bubble model, focusing on gamma-ray emission (and related comparison with Fermi), as well as thermal Sunyaev-Zel’dovich constraints.