O vi Emission from the Supernovae-regulated Interstellar Medium: Simulation versus Observation

Abstract

Abstract The O vi λλ1032, 1038 Å doublet emission traces collisionally ionized gas with K, where the cooling curve peaks for metal-enriched plasma. This warm-hot phase is usually not well-resolved in numerical simulations of the multiphase interstellar medium (ISM), but can be responsible for a significant fraction of the emitted energy. Comparing simulated O vi emission to observations is therefore a valuable test of whether simulations predict reasonable cooling rates from this phase. We calculate O vi λ1032 Å emission, assuming collisional ionization equilibrium, for our small-box simulations of the stratified ISM regulated by supernovae. We find that the agreement is very good for our solar neighborhood model, both in terms of emission flux and mean O vi density seen in absorption. We explore runs with higher surface densities and find that, in our simulations, the O vi emission from the disk scales roughly linearly with the star formation rate. Observations of O vi emission are rare for external galaxies, but our results do not show obvious inconsistency with the existing data. Assuming the solar metallicity, O vi emission from the galaxy disk in our simulations accounts for roughly 0.5% of supernovae heating.