The Survival of Multiphase Dusty Clouds in Hot Winds

TL;DR

This study uses 3D hydrodynamic simulations to investigate the survival and transformation of dusty, cold clouds in hot galactic winds, revealing conditions for their survival, destruction, or cooling, and implications for galaxy evolution.

Contribution

It provides new analytic criteria for cloud outcomes based on cooling times and cloud crushing time, and explores dust survival in multiphase galactic winds.

Findings

Cold gas can be destroyed, survive, or transform into warmer gas.

Colder clouds are entrained faster due to efficient mixing.

Dust survival depends on hot phase residence time and destruction thresholds.

Abstract

Much progress has been made recently in the acceleration of $\sim10^{4}$\,K clouds to explain absorption-line measurements of the circumgalactic medium and the warm, atomic phase of galactic winds. However, the origin of the cold, molecular phase in galactic winds has received relatively little theoretical attention. Studies of the survival of $\sim10^{4}$\,K clouds suggest efficient radiative cooling may enable the survival of expelled material from galactic disks. Alternatively, gas colder than 10$^4$\,K may form within the outflow, including molecules if dust survives the acceleration process. We explore the survival of dusty clouds in a hot wind with three-dimensional hydrodynamic simulations including radiative cooling and dust modeled as tracer particles. We find that cold $\sim10^{3}$\,K gas can be destroyed, survive, or transformed entirely to $\sim 10^4\,$K gas. We establish analytic criteria distinguishing these three outcomes which compare characteristic cooling times to the system's `cloud crushing' time. In contrast to typically studied $\sim10^{4}$\,K clouds, colder clouds are entrained faster than the drag time as a result of efficient mixing. We find that while dust can in principle survive embedded in the accelerated clouds, the survival fraction depends critically on the time dust spends in the hot phase and on the effective threshold temperature for destruction. We discuss our results in the context of polluting the circumgalactic medium with dust and metals, as well as understanding observations suggesting rapid acceleration of molecular galactic winds and ram pressure stripped tails of jellyfish galaxies.