Fading in the flow: Clouds in expanding galactic outflows

Fading in the flow: Clouds in expanding galactic outflows

«Galactic outflows, especially those triggered by intense starburst episodes, are essential agents in shaping galaxy evolution. By ejecting gas, metals, and energy into the circumgalactic medium (CGM) surrounding the galaxies, these winds regulate star formation, redistribute metals, and alter the thermodynamic state of their environments. These outflows are not uniform; instead, they are composed of gas at multiple phases, including hot/warm ionized plasma, warm/cold neutral gas, as well as dense cold molecular clouds. The evolution of cold clouds in outflows is particularly significant, as they can carry substantial mass and metals, influence star formation and feedback cycles, and shape the observable multiphase structure of outflows.  Traditionally, cloud-wind interactions have been studied through idealized “cloud-crushing” simulations, where a cold cloud is embedded in a uniform, transonic/supersonic wind – akin to a wind tunnel. Although these models provide valuable insights, they neglect a key aspect of real galactic outflows: their expansion. As outflows evolve, the winds expand adiabatically, leading to time-dependent and spatially varying background conditions that clouds experience as they are entrained and transported outward.  In this talk, I will present our recent work on cloud-crushing simulations in such expanding environments of starburst-driven galactic winds. By incorporating adiabatic expansion and realistic wind profiles, we examine how the survival, acceleration, and mixing of cold clouds differ markedly from their behavior in static, uniform backgrounds. I will highlight how cloud morphology and evolution timescales are fundamentally altered in expanding winds. I will discuss how these differences impact not only the individual clouds but also their collective dynamics, leading to significant differences in the properties of their host outflow. By contextualizing cloud-crushing in dynamically evolving environments, our work provides a more realistic framework for interpreting observations of multiphase outflows and improves our understanding of their role in galactic ecosystems.»

Sebastián López
Seminar Coordinator
DAS/UChile  – slopez@das.uchile.cl