Abstract Galactic outflows are a key agent of galaxy evolution, yet their observed multiphase nature remains difficult to reconcile with theoretical models, which often fail to explain how cold gas survives interactions with hot, fast winds. We present high-resolution 3D hydrodynamic simulations of hot outflows interacting with a multiphase interstellar medium (ISM), parameterised by its cold-gas volume filling fraction fv, depth LISM, and clump size rcl. We identify a universal survival criterion fvLISM ≳ rcrit that generalises the classical single-cloud condition (rcl rcrit) and correctly predicts cold-gas survival across diverse ISM configurations – including scale-free – down to rcl/rcrit ~ 10−2. The surviving cold phase rapidly loses memory of the initial ISM structure and evolves toward a self-similar clump mass spectrum following Zipf’s law (dN/dm∝m−2), implying that turbulent mixing and radiative condensation universally shape multiphase outflows. Cold gas assembles into plumes or confined shells of size ~χrcl, min, growing as mass is accreted from the hot phase. The interaction of a laminar wind with a clumpy ISM drives turbulence in both phases, with first-order velocity structure functions following a Kolmogorov scaling and an injection scale set by LISM, while velocity dispersions reach σ ~ cs, cold. The areal covering fraction of cold gas approaches unity even for fv ~ 10−3, though its volume filling fraction stays low, explaining the ‘misty’ appearance of observed outflows. Together, these results link small-scale cloud–wind interactions to galaxy-scale feedback, and we discuss their implications for interpreting observations and for modelling multiphase galactic winds in larger-scale simulations.
Hidalgo-Pineda et al. (Wed,) studied this question.