A Global Stability Analysis of Clusters of Galaxies with Conduction and AGN Feedback Heating

TL;DR

This paper presents a stability analysis of galaxy clusters showing that AGN feedback and conduction can stabilize cool core clusters, revealing a bimodal distribution consistent with observations of temperature profiles and AGN activity.

Contribution

First global stability analysis demonstrating AGN feedback's role in stabilizing galaxy clusters and explaining their bimodal temperature profile distribution.

Findings

AGN feedback can suppress radial instability in cool core clusters.

Clusters exhibit two stable states: cool cores stabilized by feedback and conduction, or non-cool cores stabilized by conduction.

Intermediate temperatures lead to instability, explaining observed bimodality.

Abstract

We investigate a series of steady-state models of galaxy clusters, in which the hot intracluster gas is efficiently heated by active galactic nucleus (AGN) feedback and thermal conduction, and in which the mass accretion rates are highly reduced compared to those predicted by the standard cooling flow models. We perform a global Lagrangian stability analysis. We show for the first time that the global radial instability in cool core clusters can be suppressed by the AGN feedback mechanism, provided that the feedback efficiency exceeds a critical lower limit. Furthermore, our analysis naturally shows that the clusters can exist in two distinct forms. Globally stable clusters are expected to have either: 1) cool cores stabilized by both AGN feedback and conduction, or 2) non-cool cores stabilized primarily by conduction. Intermediate central temperatures typically lead to globally unstable solutions. This bimodality is consistent with the recently observed anticorrelation between the flatness of the temperature profiles and the AGN activity (Dunn & Fabian 2008) and the observation by Rafferty et al. (2008) that the shorter central cooling times tend to correspond to significantly younger AGN X-ray cavities.