Heating and Turbulence Driving by Galaxy Motions in Galaxy Clusters

TL;DR

This study uses 3D hydrodynamic simulations to explore how galaxy motions in clusters generate turbulence and heat in the intracluster medium, revealing limits of this process in preventing cooling flows.

Contribution

It demonstrates the conditions under which galaxy motions efficiently excite turbulence and shows their limited role in halting cooling flows in galaxy clusters.

Findings

Resonant excitation of gravity waves depends on galaxy mass and number.

Velocity dispersion scales with galaxy properties in linear regime.

Galaxy motions alone cannot prevent cooling catastrophe.

Abstract

Using three-dimensional hydrodynamic simulations, we investigate heating and turbulence driving in an intracluster medium (ICM) by orbital motions of galaxies in a galaxy cluster. We consider Ng member galaxies on isothermal and isotropic orbits through an ICM typical of rich clusters. An introduction of the galaxies immediately produces gravitational wakes, providing perturbations that can potentially grow via resonant interaction with the background gas. When Ng^{1/2}Mg_11 < 100, where Mg_11 is each galaxy mass in units of 10^{11} Msun, the perturbations are in the linear regime and the resonant excitation of gravity waves is efficient to generate kinetic energy in the ICM, resulting in the velocity dispersion sigma_v ~ 2.2 Ng^{1/2}Mg_11 km/s. When Ng^{1/2}Mg_11 > 100, on the other hand, nonlinear fluctuations of the background ICM destroy galaxy wakes and thus render resonant excitation weak or absent. In this case, the kinetic energy saturates at the level corresponding to sigma_v ~ 220 km/s. The angle-averaged velocity power spectra of turbulence driven in our models have slopes in the range of -3.7 to -4.3. With the nonlinear saturation of resonant excitation, none of the cooling models considered are able to halt cooling catastrophe, suggesting that the galaxy motions alone are unlikely to solve the cooling flow problem.