Resolving the Unresolved Galactic Winds in Multiphase Models. I. Methodology and Application

Abstract Galactic winds shape galaxy evolution; however, the outflowing gas is complex: it consists of multiple ionization phases, and its properties vary spatially. Therefore, methods that combine high-fidelity observations with state-of-the-art galactic-wind models are limited. Here we investigate methods for fitting the column density profiles derived from high-quality outflow observations with the multiphase, multiscale wind model from D. B. Fielding & G. L. Bryan. We identify three key outflow parameters: the initial hot-phase mass-loading factor ( η M,hot,0 ), the initial cool-phase mass-loading factor ( η M,cool,0 ), and the initial cool-cloud mass ( M cl,0 ). We obtain good fits (reduced χ 2 < 1.5) for most galaxies, with tight constraints on η M,cool,0 and moderate constraints on the other two parameters. We find the inferred η M,cool,0 and η M,hot,0 are mostly of order unity, with significant scatter. The constraints on η M,hot,0 suggest that the interaction between the cool and hot phases allow us to indirectly constrain the properties of the hot wind from cool-outflow observations. The model also predicts various radial trends. First, for all galaxies, the cool-phase outflow velocity increases rapidly between 1 and 2 r 50 , then reaches a plateau, where r 50 is the half-light radius of the galaxy. Second, most galaxies exhibit increasing η M,cool and decreasing η M,hot with radius, with a few showing the reverse trends. These results should be interpreted as effective, model-conditional constraints but are consistent with other recent multiphase simulations and observations. This highlights that the velocity–radius mapping encoded in UV absorption profiles enables recovery of outflow spatial structures from spatially integrated spectra. Our method paves the way for future broad parameter studies and guides updates of outflow simulations in future work.