Cloud Properties in Simulated Galactic Winds

Abstract In this work, we investigate the properties of a population of cool clouds in simulated galaxy outflows. Using data from the Cholla Galactic OutfLow Simulations (or CGOLS) isolated galaxy simulations, we generate catalogs of ∼10 5 clouds. We describe the impact of two different supernova feedback models—a centrally concentrated starburst and disk-wide distributed star formation—on the resulting cloud population. In both cases we find that the mass distribution function dN / dM ∝ M −2 , in good agreement with model predictions of turbulent fragmentation. We explore how cloud properties change with distance from the galaxy and find no qualitative distinction between the two feedback modes, although significant quantitative differences exist in attributes such as the total number of clouds, their densities, etc. We further show that both internal cloud velocities and cloud–cloud relative velocities are described well by properties of turbulent motion, despite significant bulk radial velocities. Finally, we investigate the distribution of cloud sizes in the context of recent theoretical arguments about cloud survival in winds. We find that the proposed cloud survival criteria are a good predictor of cloud survival, in both the case where clouds are primarily destroyed and the case where cloud growth occurs in the outflow.