Synthetic Absorption Lines from Simulations of Multiphase Gas in Galactic Winds

Supernova-driven galactic winds are multiphase streams of gas that are often observed flowing at a range of velocities out of star-forming regions in galaxies. In this study, we use high-resolution 3D simulations of multiphase galactic winds modeled with the hydrodynamics code Cholla to investigate the connection between numerical studies and observations. Using a simulated interaction between a hot T ∼ 107 K supernova-driven wind and a cool T ∼ 104 K cloud of interstellar material, we create mock observables, including the optical depth (τ) and covering fraction (C f ), of six commonly observed ions (Si ii, C ii, Si iv, C iv, N v, and O vi) as a function of gas velocity. We compare our mock observables to surveys of galactic winds in the literature, finding good agreement with velocities and profiles of the low ions. We then compute "empirical"values for the optical depth and covering fraction following observational techniques, and compare them to the values calculated directly from the simulation data. We find that the empirically computed values tend to underestimate the "true"value of τ for ions with high optical depth and overestimate the "true"value of τ for ions with low optical depth relative to the simulated data. The empirically estimated covering fractions match our direct calculations very well for the low-ionization ions; for the high-ionization ions, the empirical covering fractions underestimate the directly computed values by up to ∼40%.