Simulations of Jet Heating in Galaxy Clusters: Successes and Challenges

TL;DR

This study uses hydrodynamical simulations to analyze how AGN jets influence cooling flows in galaxy clusters, highlighting successes in reducing cooling rates and challenges related to numerical convergence and multi-phase gas modeling.

Contribution

It introduces novel analysis methods for measuring heating and cooling rates and demonstrates the effects of kinetic jets on cooling flows in galaxy clusters.

Findings

Kinetic jets significantly reduce cooling rates within 20 kpc.

Jet feedback is anisotropic, mainly along the jet axis.

Turbulent heating is only significant near the cluster center.

Abstract

We study how jets driven by active galactic nuclei influence the cooling flow in Perseus-like galaxy cluster cores with idealised, non-relativistic, hydrodynamical simulations performed with the Eulerian code ATHENA using high-resolution Godunov methods with low numerical diffusion. We use novel analysis methods to measure the cooling rate, the heating rate associated to multiple mechanisms, and the power associated with adiabatic compression/expansion. A significant reduction of the cooling rate and cooling flow within 20 kpc from the centre can be achieved with kinetic jets. However, at larger scales and away from the jet axis, the system relaxes to a cooling flow configuration. Jet feedback is anisotropic and is mostly distributed along the jet axis, where the cooling rate is reduced and a significant fraction of the jet power is converted into kinetic power of heated outflowing gas. Away from the jet axis weak shock heating represents the dominant heating source. Turbulent heating is significant only near the cluster centre, but it becomes inefficient at 50 kpc scales where it only represents a few percent of the total heating rate. Several details of the simulations depend on the choice made for the hydro solver, a consequence of the difficulty of achieving proper numerical convergence for this problem: current physics implementations and resolutions do not properly capture multi-phase gas that develops as a consequence of thermal instability. These processes happen at the grid scale and leave numerical solutions sensitive to the properties of the chosen hydro solver.