Cosmic Ray Feedback

TL;DR

This paper explores how cosmic rays from cavities in hot cluster gas influence cluster dynamics, including heating, buoyancy, and suppression of cooling flows, through various physical processes.

Contribution

It introduces a comprehensive model of cosmic ray feedback mechanisms in galaxy clusters, highlighting their role in regulating cooling and gas transport.

Findings

Cosmic rays drive shocks that increase local entropy.

Cavities produce thermal filaments and diffuse cosmic rays.

Cosmic ray buoyancy transports low entropy gas outward.

Abstract

Cosmic rays produced or deposited at sites in hot cluster gas are thought to provide the pressure that forms X-ray cavities. While cavities have a net cooling effect on cluster gas, young, expanding cavities drive shocks that increase the local entropy. Cavities also produce radial filaments of thermal gas and are sources of cluster cosmic rays that diffuse through cavity walls, as in Virgo where a radio lobe surrounds a radial thermal filament. Cosmic rays also make the hot gas locally buoyant, allowing large masses of low entropy gas to be transported out beyond the cooling radius. Successive cavities maintain a buoyant outflow that preserves the cluster gas temperature and gas fraction profiles and dramatically reduces the cooling rate onto the central black hole.