Simulating the Cooling Flow of Cool-Core Clusters

TL;DR

This study uses high-resolution simulations to explore cooling flows in cool-core clusters, revealing a stable, smooth flow outside the core and rapid central cooling leading to accretion disk formation, with implications for AGN feedback mechanisms.

Contribution

It provides detailed high-resolution simulations of cool-core clusters without AGN heating, highlighting the natural development of a cooling catastrophe confined to the central 100 pc and the importance of resolution and galaxy potential.

Findings

Cooling catastrophe occurs only in the central 10-100 pc.

Outer regions exhibit smooth, instability-free cooling consistent with observations.

Including the brightest cluster galaxy's potential is crucial for accurate results.

Abstract

We carry out high-resolution adaptive mesh refinement simulations of a cool core cluster, resolving the flow from Mpc scales down to pc scales. We do not (yet) include any AGN heating, focusing instead on cooling in order to understand how gas gets to the supermassive black hole (SMBH) at the center of the cluster. We find that, as the gas cools, the cluster develops a very flat temperature profile, undergoing a cooling catastrophe only in the central 10-100 pc of the cluster. Outside of this region, the flow is smooth, with no local cooling instabilities, and naturally produces very little low-temperature gas (below a few keV), in agreement with observations. The gas cooling in the center of the cluster rapidly forms a thin accretion disk. The amount of cold gas produced at the very center grows rapidly until a reasonable estimate of the resulting AGN heating rate (assuming even a moderate accretion efficiency) would overwhelm cooling. We argue that this naturally produces a thermostat which links the cooling of gas out to 100 kpc with the cold gas accretion in the central 100 pc, potentially closing the loop between cooling and heating. Isotropic heat conduction does not affect the result significantly, but we show that including the potential well of the brightest cluster galaxy is necessary to obtain the correct result. Also, we found that the outcome is sensitive to resolution, requiring very high mass resolution to correctly reproduce the small transition radius.