The kinematic and thermodynamic state of clouds in complex wind–multicloud environments

In this talk I present our study of the interaction between a shock-driven hot wind and a cold multicloud layer, under conditions representative of interstellar and circumgalactic gas, using a suite of hydrodynamical simulations. We employ a friends-of-friends algorithm to identify distinct clouds, and by tracing their evolution, the method provides comprehensive descriptions of cloud morphology, including measures of elongation and fractal dimension. Combined with the kinematics, these allow us to refine previous models for drag and entrainment.

We find that while ram pressure dominates momentum transfer at early times, condensation becomes increasingly important after the initial shock passage. Internal cloud motions are found to generate an effective dynamic pressure exceeding thermal pressure by an order of magnitude, sustaining a multiphase outflow. I present a systematic study of how these results vary with the geometry of the initial cloud distribution and the wind velocity.

Finally, applying our analysis to HI-emitting gas, correcting for beam size and telescope sensitivity, reconciles two observed populations of HI clouds in the Milky Way nuclear wind as structures belonging to the same continuous outflow.