Survival of higher overdensity cold gas in a turbulent, multiphase medium

TL;DR

This study uses 3D simulations to investigate the survival of high-density cold gas clouds in turbulent hot media, revealing that efficient cooling is crucial for their longevity and proposing a new survival criterion.

Contribution

The paper introduces a new survival criterion for cold gas clouds in turbulent media, showing that higher overdensity clouds require more efficient cooling to survive.

Findings

Cloud survival occurs only when cooling-to-cloud-crushing ratio is below 0.01.

Higher overdensity clouds are less likely to survive turbulence without efficient cooling.

The traditional survival boundary of ratio ~1 is not applicable for high-density clouds.

Abstract

Cold gas clouds embedded in a hot, turbulent medium are expected to be short-lived due to disruptive hydrodynamic instabilities. However, radiative cooling might allow such clouds to survive and grow. We present 3D \texttt{Athena++} simulations of clouds with a density contrast of $\chi = 1000$, exploring turbulent Mach numbers $\mathcal{M}\in (0.25, 0.75)$ and cloud radii chosen to span cooling-to-crushing ratios $\alpha \in [0.001, 10]$. We find a shift in the survival boundary, with cloud survival occurring only when the cooling-to-cloud-crushing ratio ($t_{\text{cool,mix}} / t_{\text{cc}}$) $\lesssim 0.01$, which is lower than the expected boundary of $\sim 1$. This result shows that it is more difficult for higher over-density cold clouds to survive in a turbulent, hot medium, and suggests another `survival criterion'.