Can spiral flow topologies sustain overdense filaments in galactic-wind cloud interaction?

In this Letter, we investigate the local kinematic organization of the cloud–wake region in a three-dimensional Mach 7.5 galactic-wind cloud interaction using the PLUTO code [Mignone et al., “PLUTO: A numerical code for computational astrophysics,” Astrophys. J. Suppl. Ser. 170, 228 (2007)]. Velocity-gradient tensor analysis reveals near-wake dominance of compressive–spiral (Unstable-Focus-Compressing) structures generated by shock compression, while downstream evolution exhibits coexistence with stretching–spiral (Stable-Focus-Stretching) structures. The topology fractions FUFC and FSFS increase globally downstream, whereas within overdense regions FUFC(ρ>ρth) decreases and FSFS(ρ>ρth) increases with increasing strain–compressibility ratio χ, demonstrating progressive stretching-dominated reorganization of dense vortical structures into coherent filaments. Simultaneously, decreasing density variance and increasing helicity localization within overdense regions indicate sustained velocity–vorticity alignment, showing that spiral flow topologies can dynamically sustain overdense filaments in compressible galactic outflows.