Simulated Observations of Multiphase Galactic Winds

TL;DR

This paper uses high-resolution 3D simulations to connect the properties of multiphase galactic winds with observations, revealing how empirical methods can misestimate ion optical depths.

Contribution

It introduces a detailed simulation approach to compare mock observables with actual data, highlighting biases in observational techniques for measuring ion optical depths.

Findings

Good agreement with observed velocities and profiles of low ions.

Empirical optical depth estimates often underestimate or overestimate true values.

Simulation results help calibrate observational measurements of galactic winds.

Abstract

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 $T\sim 10^{7}\,\rm K$ supernova-driven wind and a cool $T\sim 10^{4}\,\rm K$ cloud of interstellar material, we create mock observables, including the optical depth and covering fraction 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 $\tau$ for ions with high optical depth, and overestimate the "true" value of $\tau$ for ions with low optical depth, relative to the simulated data.