A multifiltering study of turbulence in a large sample of simulated galaxy clusters

Abstract

We present results from a large set of N-body/SPH hydrodynamical cluster simulations aimed at studying the statistical properties of turbulence in the ICM. The numerical hydrodynamical scheme employs a SPH formulation in which gradient errors are strongly reduced by using an integral approach. We consider both adiabatic and radiative simulations. We construct clusters subsamples according to the cluster dynamical status or gas physical modeling, from which we extract small-scale turbulent velocities obtained by applying to cluster velocities different multiscale filtering methods. The velocity power spectra of non-radiative relaxed clusters are mostly solenoidal and steeper than Kolgomorov. Cooling runs are distinguished by much shallower spectra, a feature which we interpret as the injection of turbulence at small scales due to the interaction of compact cool gas cores with the ICM. Turbulence in galaxy clusters is then characterized by multiple injection scales, with the small scale driving source acting in addition to the large scale injection mechanisms. Cooling runs of relaxed clusters exhibit enstrophy profiles with a power-law behavior over more than two decades in radius, and a turbulent-to-thermal energy ratio ~1 %. In accord with Hitomi observations, in the core of a highly relaxed cluster we find low level of gas motions. In addition, the estimated cluster radial profile of the sloshing oscillation period exhibits an associated Froude number satisfying Fr ~ 0.1 within r / r_{200} <~ 0.1. Our findings suggest that in cluster cores ICM turbulence approaches a stratified anisotropic regime, with weak stirring motions dominated by gravity buoyancy forces and strongly suppressed along the radial direction. We conclude that turbulent heating cannot be considered the main heating source in cluster cores.