Testing the ergodicity of star formation within galaxies

Abstract

Part of our understanding of how galaxies evolve is based on individual evolutions inferred from population trends. In its strictest form, this approach implicitly assumes that the star formation properties of galaxies exhibit ergodic behaviours, such that the time averages of individual galaxies are equivalent to the average of the population at any given time. In this thesis, we analyze the validity of this assumption on simulated galaxies modelled after observed ones. We find that galaxies without stellar wind feedback are able to match observations and do not, in general, follow strictly ergodic star formation histories. Partial ergodicity is presented in an astronomical sense for the first time, in which subsets of galaxies exhibit time evolution broadly similar to ensemble averages when averaged over, and is observed in the modelled galaxies. Future studies are needed to include the impact of mergers, alternative feedback and stellar evolution models, and ideally a larger sample.