The Interplay of Kinetic and Radiative Feedback in Galaxy Clusters

Abstract

Recent observations provide evidence that some cool-core clusters host quasars in their brightest cluster galaxies (BCGs). Motivated by these findings, we use 3D radiation-hydrodynamic simulations with the code Enzo to explore the joint role of kinetic and radiative feedback from supermassive black holes (SMBHs) in BCGs. We implement kinetic feedback as subrelativistic plasma outflows and model radiative feedback using ray-tracing radiative transfer or thermal energy injection. In our simulations, the central SMBH transitions between the radiatively efficient and radiatively inefficient states on timescales of a few gigayears, as a function of its accretion rate. The timescale for this transition depends primarily on the fraction of power allocated to each feedback mode, and to a lesser degree on the overall feedback luminosity of the active galactic nucleus (AGN). Specifically, we find that (a) kinetic feedback must be present at both low and high accretion rates in order to prevent the cooling catastrophe, and (b) its contribution likely accounts for >10% of the total AGN feedback power, because below this threshold simulated BCGs tend to host radio-loud quasars most of the time, in apparent contrast with observations. We also find a positive correlation between the AGN feedback power and the mass of the cold gas filaments in the cluster core, indicating that observations of H α filaments can be used as a measure of AGN feedback.