AGN Heating in Simulated Cool-Core Clusters

TL;DR

This paper investigates how AGN feedback heats cool-core galaxy clusters by analyzing shock waves, turbulence, and mixing processes in simulations, revealing the dominant heating mechanisms and their spatial distribution over time.

Contribution

It provides a detailed analysis of the relative roles of shock heating, turbulence, and mixing in AGN feedback within simulated cool-core clusters, highlighting the importance of shock dissipation and cyclical heating processes.

Findings

Shock energy dissipation exceeds turbulence by nearly an order of magnitude.

Most shocks are weak with Mach numbers below 1.5, but stronger shocks dissipate more energy.

Heating processes vary spatially and temporally, explaining different observed cluster behaviors.

Abstract

We analyze heating and cooling processes in an idealized simulation of a cool-core cluster, where momentum-driven AGN feedback balances radiative cooling in a time-averaged sense. We find that, on average, energy dissipation via shock waves is almost an order of magnitude higher than via turbulence. Most of the shock waves in the simulation are very weak shocks with Mach numbers smaller than 1.5, but the stronger shocks, although rare, dissipate energy more effectively. We find that shock dissipation is a steep function of radius, with most of the energy dissipated within 30 kpc, while radiative cooling loses area less concentrated. However, adiabatic processes and mixing (of post-shock materials and the surrounding gas) are able to redistribute the heat throughout the core. A considerable fraction of the AGN energy also escapes the core region. The cluster goes through cycles of AGN outbursts accompanied by periods of enhanced precipitation and star formation, over Gyr timescales. The cluster core is under-heated at the end of each cycle, but over-heated at the peak of the AGN outburst. During the heating-dominant phase, turbulent dissipation alone is often able to balance radiative cooling at every radius but, when this is occurs, shock waves inevitably dissipate even more energy. Our simulation explains why some clusters, such as Abell 2029, are cooling dominated, while in some other clusters, such as Perseus, various heating mechanisms including shock heating, turbulent dissipation and bubble mixing can all individually balance cooling, and together, overheat the core.