AGN Heating, Thermal Conduction, and the Sunyaev‐Zel'dovich Effect in Galaxy Groups and Clusters

Abstract

We investigate in detail the role of active galactic nuclei (AGNs) in the physical state of the gas in galaxy groups and clusters, and the implications for anisotropy in the cosmic microwave background (CMB) from the Sunyaev-Zel'dovich (SZ) effect. We have recently shown that AGNs can significantly change the entropy of the intracluster medium (ICM) and explain the observations of excess entropy in groups and clusters. AGNs are assumed to deposit energy via buoyant bubbles that expand as they rise in the cluster atmosphere and do P dV work on the ICM. Here we include the effect of thermal conduction and find that the resulting profiles of temperature and entropy are consistent with observations. Unlike previously proposed models, our model predicts that isentropic cores are not an inevitable consequence of preheating. The model also reproduces the observational trend for the density profiles to flatten in lower mass systems. We deduce the energy (Eagn) required to explain the entropy observations as a function of mass of groups and clusters (Mcluster) and show that Eagn ∝ M with α ~ 1.5. We demonstrate that the entropy measurements, in conjunction with our model, can be translated into constraints on the cluster-black hole mass relation. The inferred relation is nonlinear and has the form Mbh ∝ M. This scaling is an analog and extension of a similar relation between the black hole mass and the galactic halo mass that holds on smaller scales. In addition, we study the implications of these results for the thermal SZ effect. We show that the central decrement of the CMB temperature is reduced due to the enhanced entropy of the ICM and that the decrement predicted from the plausible range of energy input from the AGN is consistent with available data on the SZ decrement. We also estimate the Poisson contribution to the angular power spectrum of the CMB from the SZ effect due to AGN heating. We show that AGN heating, combined with the observational constraints on entropy, leads to suppression of higher multipole moments in the power spectrum, and we find that this effect is stronger than previously thought. The suppression in the power spectrum in our model is due to depletion of gas from the central regions that is more efficient in low-mass clusters and groups than in massive clusters.