Cloud Crushing and Dissipation of Uniformly-Driven Adiabatic Turbulence in Circumgalactic Media

TL;DR

This study uses extensive numerical simulations to analyze how turbulence in the circumgalactic medium dissipates energy, revealing distinct behaviors based on temperature and velocity, and providing new data for future galaxy-scale modeling.

Contribution

It introduces a comprehensive dataset of turbulence dissipation timescales considering kinematics and thermodynamics, enhancing understanding of gas dynamics in the circumgalactic medium.

Findings

Hot, subsonic turbulence shows slow dissipation and minimal density fluctuations.

Warm, supersonic turbulence results in rapid cooling and significant density clumping.

Density contrasts decay within 30-300 Myr after turbulence stops.

Abstract

The circumgalactic medium (CGM) is responsive to kinetic disruptions generated by nearby astrophysical events. In this work, we study the saturation and dissipation of turbulent hydrodynamics within the CGM through an extensive array of 252 numerical simulations with a large parameter space. These simulations are endowed with proper cooling mechanisms to consistently explore the parameter space spanned by the average gas density, metallicity, and turbulence driving strength. A dichotomy emerges in the dynamics dissipation behaviors. Disturbances that are hot and subsonic are characterized by weak compression and slow dissipation, resulting in density fluctuations typically $\lesssim 10^{-2}$. Conversely, warm supersonic turbulence, marked by significant compression shocks and subsequent rapid cooling, is associated with substantial clumping factors $\sim 10^0-10^1$. In the supersonic cases, the kinetic energy decay is divided into a rate-limiting phase of shock dissipation and a comparatively swift phase of thermal dissipation, predominantly occurring within the overdense regions. Upon turbulence driving turnoff, the strong density contrasts decay within a relatively brief timescale of $\sim 30 - 300~{\rm Myr}$, depending on the average gas density. Dense clouds are crushed on similar timescales of $ \sim 30 - 100 ~{\rm Myr} $, depending on turbulence driving strength but independent from average gas density. Results of this work also contribute a novel dataset of dissipation timescales that incorporates an understanding of kinematics and thermodynamics in addition to the traditional cooling rate tables, which may serve as a valuable asset for forthcoming simulations that aim to explore gas dynamics on galactic and cosmological scales.