Self-Regulation of AGN in Galaxy Clusters

TL;DR

This study uses advanced 3D hydrodynamical simulations to explore how AGN feedback self-regulates heating and cooling in galaxy cluster cores, highlighting the role of turbulence in this process.

Contribution

It introduces a novel simulation approach incorporating RT-driven turbulence to model AGN feedback self-regulation in galaxy clusters.

Findings

AGN feedback maintains thermal balance over billions of years.

Recurrence times of AGN outbursts are approximately 80 Myrs.

Turbulence is crucial for effective self-regulation in cluster cores.

Abstract

Cool cores of galaxy clusters are thought to be heated by low-power active galactic nuclei (AGN), whose accretion is regulated by feedback. However, the interaction between the hot gas ejected by the AGN and the ambient intracluster medium is extremely difficult to simulate as it involves a wide range of spatial scales and gas that is Rayleigh-Taylor (RT) unstable. Here we present a series of three-dimensional hydrodynamical simulations of a self-regulating AGN in a galaxy cluster. Our adaptive-mesh simulations include prescriptions for radiative cooling, AGN heating and a subgrid model for RT-driven turbulence, which is crucial to simulate this evolution. AGN heating is taken to be proportional to the rest-mass energy that is accreted onto the central region of the cluster. For a wide range of feedback efficiencies, the cluster regulates itself for at least several $10^9$ years. Heating balances cooling through a string of outbursts with typical recurrence times of around 80 Myrs, a timescale that depends only on global cluster properties. Under certain conditions we find central dips in the metallicity of the intracluster medium. Provided the sub-grid model used here captures all its key properties, turbulence plays an essential role in the AGN self-regulation in cluster cores.