Acoustic Disturbances in Galaxy Clusters

TL;DR

This paper investigates the role of acoustic wave dissipation as a heating mechanism in galaxy cluster cores, emphasizing the importance of reduced transport coefficients for effective wave heating.

Contribution

It revisits wave dissipation processes in galaxy clusters, incorporating electron-ion temperature differences and kinetic effects, reaffirming the significance of low transport coefficients for wave heating.

Findings

Reduced transport coefficients are crucial for wave heating effectiveness.

Electron and ion temperature perturbations evolve separately in wave dissipation.

Kinetic effects can be estimated by semi-collisionless theory.

Abstract

Galaxy cluster cores are pervaded by hot gas which radiates at far too high a rate to maintain any semblance of a steady state; this is referred to as the cooling flow problem. Of the many heating mechanisms that have been proposed to balance radiative cooling, one of the most attractive is dissipation of acoustic waves generated by Active Galactic Nuclei (AGN). Fabian (2005) showed that if the waves are nearly adiabatic, wave damping due to heat conduction and viscosity must be well below standard Coulomb rates in order to allow the waves to propagate throughout the core. Because of the importance of this result, we have revisited wave dissipation under galaxy cluster conditions in a way that accounts for the self limiting nature of dissipation by electron thermal conduction, allows the electron and ion temperature perturbations in the waves to evolve separately, and estimates kinetic effects by comparing to a semi-collisionless theory. While these effects considerably enlarge the toolkit for analyzing observations of wavelike structures and developing a quantitative theory for wave heating, the drastic reduction of transport coefficients proposed in Fabian (2005) remains the most viable path to acoustic wave heating of galaxy cluster cores.