Hydrodynamics of Clustered Clouds: Drafting, Survival, Condensation, and Ablation

Abstract

Abstract For et al., who catalogued Magellanic Stream (MS) clouds, suggested that there is substantial large-scale turbulence in the MS. Here we follow up with a series of FLASH simulations that model the hydrodynamic effects that clouds have on each other. The suite of simulations includes a range of cloud separation distances and densities. The ambient conditions are similar to those surrounding the MS but also relevant to the circumgalactic medium and intergalactic medium. Ten simulations are presented, eight of which model clustered clouds and two of which model isolated clouds. The isolated clouds are used as controls for comparison with the multicloud simulations. We find that if the clouds are initially near each other, then hydrodynamical drafting helps the trailing cloud to catch the leading cloud and mix together. We present the measured acceleration due to drafting and find that lower-density clouds in lower-density environments experience more acceleration due to drafting than their denser cohorts. We find that the clustering of clouds also increases the condensation of ambient material and affects longevity. We analyze the velocity dispersion of the clouds using a single component method and a multicomponent decomposition method. We find that the presence of a second cloud increases the velocity dispersion behind the trailing cloud at some times. We find that the velocity dispersion due to gas motion in our simulations is significantly less than the actual dispersion observed by For et al., indicating that the thermal component must dominate in the MS.