The Turbulent Destruction of Clouds - II. Mach Number Dependence, Mass-loss Rates, and Tail Formation

TL;DR

This study investigates how Mach number influences the turbulent destruction of clouds by shocks, revealing that Kelvin-Helmholtz instabilities dominate mass loss and that cloud lifetime is significantly longer than previous estimates, with implications for hot-cool phase interactions.

Contribution

It demonstrates that Kelvin-Helmholtz instabilities are the primary mechanism for cloud destruction, revises cloud lifetime estimates, and explores the effects of Mach number and density contrast on cloud-shock interactions.

Findings

Kelvin-Helmholtz instabilities dominate cloud destruction.

Cloud lifetime is about 6 times the KH growth timescale.

Long tail formation occurs only at high density contrasts.

Abstract

The turbulent destruction of a cloud subject to the passage of an adiabatic shock is studied. We find large discrepancies between the lifetime of the cloud and the analytical result of Hartquist et al. (1986). These differences appear to be due to the assumption in Hartquist et al. that mass-loss occurs largely as a result of lower pressure regions on the surface of the cloud away from the stagnation point, whereas in reality Kelvin-Helmholtz (KH) instabilities play a dominant role in the cloud destruction. We find that the true lifetime of the cloud (defined as when all of the material from the core of the cloud is well mixed with the intercloud material in the hydrodynamic cells) is about 6 times t_KHD, where t_KHD is the growth timescale for the most disruptive, long-wavelength, KH instabilities. These findings have wide implications for diffuse sources where there is transfer of material between hot and cool phases. The properties of the interaction as a function of Mach number and cloud density contrast are also studied. The interaction is milder at lower Mach numbers with the most marked differences occuring at low shock Mach numbers when the postshock gas is subsonic with respect to the cloud (i.e. M < 2.76). Material stripped off the cloud only forms a long "tail-like" feature if the density contrast of the cloud to the ambient medium, chi > 1e3.