HYDRODYNAMICAL COUPLING of MASS and MOMENTUM in MULTIPHASE GALACTIC WINDS

Using a set of high-resolution hydrodynamical simulations run with the Cholla code, we investigate how mass and momentum couple to the multiphase components of galactic winds. The simulations model the interaction between a hot wind driven by supernova explosions and a cooler, denser cloud of interstellar or circumgalactic media. By resolving scales of δx < 0.1 pc over 100 pc distances, our calculations capture how the cloud disruption leads to a distribution of densities and temperatures in the resulting multiphase outflow and quantify the mass and momentum associated with each phase. We find that the multiphase wind contains comparable mass and moment a in phases over a wide range of densities and temperatures extending from the hot wind (n ≈ 10^-2.5 cm^-3, T ≈ 10^6.5 K) to the coldest components (n ≈ 10² cm^-3, T ≈ 10² K). We further find that the momentum distributes roughly in proportion to the mass in each phase, and the mass loading of the hot phase by the destruction of cold, dense material is an efficient process. These results provide new insight into the physical origin of observed multiphase galactic outflows and inform galaxy formation models that include coarser treatments of galactic winds. Our results confirm that cool gas observed in outflows at large distances from the galaxy (≳1 kpc) likely does not originate through the entrainment of cold material near the central starburst.