The turbulent destruction of clouds - II. Mach number dependence, mass-loss rates and tail formation

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. 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 x t(KHD), where t(KHD) is the growth time-scale 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 the Mach number and cloud density contrast are also studied. The interaction is milder at lower Mach numbers with the most marked differences occurring at low shock Mach numbers when the post-shock 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 chi greater than or similar to 10(3).