Turbulence in the ICM from mergers, cool-core sloshing and jets: results from a new multi-scale filtering approach

TL;DR

This paper introduces a new multi-scale filtering method to identify and analyze turbulence in hydrodynamical simulations of galaxy clusters, revealing the nature and driving mechanisms of turbulence in the intra-cluster medium.

Contribution

The paper presents a robust, fast multi-scale filtering technique that does not assume a coherence scale, enabling detailed analysis of turbulence in various astrophysical simulation scenarios.

Findings

Turbulence in galaxy clusters is mostly tangential near the center and isotropic near the virial radius.

AGN jets induce predominantly radial turbulence motions.

Turbulent diffusivity in the intra-cluster medium ranges from 10^29 to 10^30 cm^2/s.

Abstract

We have designed a simple multi-scale method that identifies turbulent motions in hydrodynamical grid simulations. The method does not assmume ant a-priori coherence scale to distinguish laminar and turbulent flows. Instead, the local mean velocity field around each cell is reconstructed with a multi-scale filtering technique, yielding the maximum scale of turbulent eddies by means of iterations. The method is robust, fast and easily applicable to any grid simulation. We present here the application of this technique to the study of spatial and spectral properties of turbulence in the intra cluster medium, measuring turbulent diffusion and anisotropy of the turbulent velocity field for a variety of driving mechanisms: a) accretion of matter in galaxy clusters (simulated with ENZO); b) sloshing motions around cool-cores (simulated with FLASH); c) jet outflows from active galactic nuclei, AGN (simulated with FLASH). The turbulent velocities driven by matter accretion in galaxy clusters are mostly tangential in the inner regions (inside the cluster virial radius) and isotropic in regions close to the virial radius. The same is found for turbulence excited by cool core sloshing, while the jet outflowing from AGN drives mostly radial turbulence motions near its sonic point and beyond. Turbulence leads to a diffusivity in the range =10^29-10^30 cm^2/s in the intra cluster medium. On average, the energetically dominant mechanism of turbulence driving in the intra cluster medium is represented by accretion of matter and major mergers during clusters evolution.