Turbulence production and turbulent pressure support in the intergalactic medium

TL;DR

This study uses hydrodynamical simulations with a subgrid turbulence model to analyze turbulence production and its role in supporting the intergalactic medium against gravity, revealing different mechanisms in the ICM and WHIM.

Contribution

It introduces a detailed simulation-based analysis of turbulence sources and their dynamical importance in the intergalactic medium, highlighting differences between ICM and WHIM.

Findings

Turbulence in the ICM is mainly produced by merger shear flows.

In the WHIM, shock interactions dominate turbulence production.

Non-thermal pressure support is significant only locally, not widespread.

Abstract

The injection and evolution of turbulence in the intergalactic medium is studied by means of mesh-based hydrodynamical simulations, including a subgrid scale (SGS) model for small-scale unresolved turbulence. The simulations show that the production of turbulence has a different redshift dependence in the intracluster medium (ICM) and the warm-hot intergalactic medium (WHIM). We show that turbulence in the ICM is produced chiefly by merger-induced shear flows, whereas the production in the WHIM is dominated by shock interactions. Secondly, the effect of dynamical pressure support on the gravitational contraction has been studied. This turbulent support is stronger in the WHIM gas at baryon overdensities 1 < delta < 100, and less relevant for the ICM. Although the relative mass fraction of the gas with large vorticity is considerable (52% in the ICM), we find that for only about 10% in mass this is dynamically relevant, namely not associated to an equally large thermal pressure support. According to this result, a significant non-thermal pressure support counteracting the gravitational contraction is a localised characteristic in the cosmic flow, rather than a widespread feature.