On the kinematic and thermodynamic state of clouds in complex wind–multicloud environments using a friends-of-friends analysis
Year: 2025
Type: article
Abstract: ABSTRACT We investigate the interaction between a shock-driven hot wind and a cold multicloud layer, for conditions commonly found in interstellar and circumgalactic gas. We present a method for identifying distinct clouds using a friends-of-friends algorithm. This approach unveils novel detailed information about individual clouds and their collective behaviour. By tracing the evolution of individual clouds, our method provides comprehensive descriptions of cloud morphology, including measures of the elongation and fractal dimension. Combining the kinematics and morphology of clouds, we refine previous models for drag and entrainment processes. Our by-cloud analysis allows to discern the dominant entrainment processes at different times. We find that after the initial shock passage, momentum transfer due to condensation becomes increasingly important, compared to ram pressure, which dominates at early times. We also find that internal motions within clouds act as an effective dynamic pressure that exceeds the thermal pressure by an order of magnitude. Our analysis shows how the highly efficient cooling of the warm mixed gas at temperatures $\sim 10^{5}$ K is effectively balanced by the kinetic energy injected by the hot wind into the warm and cold phases via shocks and shear motions. Compression-driven condensation and turbulence dissipation maintain a multiphase outflow and can help explain the presence of dense gas in galaxy-scale winds. Finally, we show that applying our friends-of-friends analysis to H i-emitting gas and correcting for beam size and telescope sensitivity can explain two populations of H i clouds within the Milky-Way nuclear wind as structures pertaining to the same outflow.
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: gold
Estimated APC paid: $3,046
Funders: California Department of Fish and Game, National Computational Infrastructure, Iowa Science Foundation, Deutscher Akademischer Austauschdienst, Deutsche Forschungsgemeinschaft, Israel Science Foundation, Secretaría de Educación Superior, Ciencia, Tecnología e Innovación, Gauss Centre for Supercomputing, Australian Research Council, Leibniz-Gemeinschaft, Leibniz-Rechenzentrum
Awards: G1068045743, G1437092994, G1897041155, G2485229595, G2684241402, G2697985630, Radiation-Driven Turbulence and Star Formation, G3662810328, Star Formation Through Cosmic Time, G4066435496, G432818845, EXC 2094: ORIGINS: Vom Ursprung des Universums bis zu den ersten Bausteinen des Lebens, G5204036440, G6523260978, G6776639944, G6781880672, G6945796520, G696353817, EXC 2121: Quantum Universe, G823906859, G8709026768
OpenAlex ID: W4411204914