The galactic scale impact of feedback from individual stars

Abstract: Feedback from stars is essential for the formation and evolution of galaxies. It is an energy source that drives gas motions and chemically enriches the galaxy by supplying metals. Without this stellar feedback, numerical galaxy simulations result in galaxies with little resemblance to those observed in our Universe. Modern galaxy simulations frequently reach a mass resolution of a few tens of solar masses. Such high-resolution warrants models incorporating individual stars. These models enable a detailed treatment of when and where stars inject feedback. In this thesis, I present such a model and provide a series of papers exploring physical mechanisms unlocked by this model.In paper I, we investigate how runaway stars affect the galactic winds driven by stellar feedback in Milky Way-like galaxies. Massive runaway stars can venture to places where these short-lived stars are otherwise not found (e.g., between spiral arms). In these regions of diffuse gas, supernovae can efficiently incorporate energy into large volumes of gas, thereby boosting the gas outflow rate of the galaxy. Furthermore, the star formation rate is not significantly affected since parts of the feedback budget move away from star-forming gas. The result is a ten-fold boost in the mass loading factor.Paper II is a follow-up investigation of a surprising signal of star formation in spiral galaxies with runaway stars, found in Paper I. The signal is produced by the rapid migration of runaway stars to the galaxy's outskirts. Via direct comparison to observational data, we find that this explains faint far-ultraviolet radiation detected outside the optical radius of nearby spiral galaxies. This radiation manifests as a trend in the star formation relation with a slope similar to one produced by runaway stars escaping to these regions.In paper III, the star-by-star model is upgraded with a more advanced model for feedback and runaway stars. We showcase this model with a suit of simulations of isolated dwarf galaxies, testing a range of parameters for the natal velocity model of individual stars responsible for incorporating runaway stars. In stark contrast to the Milky Way-like galaxy, we find runaway stars play little to no role in determining outflows in dwarf galaxies. We discuss several possible reasons for the different effects in small and large galaxies.