Turbulence driven by structure formation in the circum-galactic medium

TL;DR

This study uses hydrodynamic simulations with a subgrid turbulence model to analyze how structure formation drives turbulence in the circum-galactic medium at redshift 2, affecting the warm-hot intergalactic medium and filaments.

Contribution

It introduces a detailed simulation approach incorporating a subgrid turbulence model to quantify turbulence effects driven solely by structure formation in the circum-galactic medium.

Findings

Turbulence impacts mainly the warm-hot intergalactic medium around shock-heated structures.

The ratio of turbulent to thermal pressure in the WHIM is about 0.1.

Turbulence influence increases with gas density in the diffuse intergalactic medium.

Abstract

The injection of turbulence in the circum-galactic medium at redshift z = 2 is investigated using the mesh-based hydrodynamic code Enzo and a subgrid-scale (SGS) model for unresolved turbulence. Radiative cooling and heating by a uniform Ultraviolet (UV) background are included in our runs and compared with the effect of turbulence modelling. Mechanisms of gas exchange between galaxies and the surrounding medium, as well as metal enrichment, are not taken into account, and turbulence is here driven solely by structure formation (mergers and shocks). We find that turbulence, both at resolved and SGS scales, impacts mostly the warm-hot intergalactic medium (WHIM), with temperature between 10^5 and 10^7 K, mainly located around collapsed and shock heated structures, and in filaments. Typical values of the ratio of turbulent to thermal pressure is 0.1 in the WHIM, corresponding to a volume-weighted average of the SGS turbulent to thermal Doppler broadening b_t / b_therm = 0.26, on length scales below the grid resolution of 25 kpc/h. In the diffuse intergalactic medium (IGM), defined in a range of baryon overdensity \delta\ between 1 and 50, the importance of turbulence is smaller, but grows as a function of gas density, and the Doppler broadening ratio is fitted by the function b_t / b_therm = 0.023 \delta^{0.58}.