In this thesis we used numerical simulations to explore the role that chemistry plays in galaxy formation. Simulations of galaxies often assume chemical equilibrium, where the chemical reactions... Show moreIn this thesis we used numerical simulations to explore the role that chemistry plays in galaxy formation. Simulations of galaxies often assume chemical equilibrium, where the chemical reactions between ions and molecules have reached a steady state. However, this assumption may not be valid if the physical conditions of the gas are evolving rapidly. Therefore, we developed a chemical model to follow the non-equilibrium evolution of ions and molecules. We then incorporated this model into hydrodynamic simulations of galaxies. We ran simulations with different metallicities (i.e. different proportions of heavy elements) and UV radiation fields, first using our full non-equilibrium chemical model and then assuming chemical equilibrium. We found that the total star formation rate is higher at higher metallicity and for weaker radiation fields. In contrast, non-equilibrium chemistry does not strongly influence the total star formation rate or outflow properties of the galaxy. However, it does affect the abundances of individual chemical species, for example in molecular outflows. Finally, we explored the properties of molecular clouds in our simulations. At low metallicity, the molecular fraction of young clouds tends to be below equilibrium, as the molecules are still forming. This also affects the observable CO emission from young clouds. Show less
Ten billion years ago the Universe was at the peak of its star formation activity, which has been declining since then. This thesis investigates, with novel spectroscopic data from Hubble Space... Show moreTen billion years ago the Universe was at the peak of its star formation activity, which has been declining since then. This thesis investigates, with novel spectroscopic data from Hubble Space Telescope, the evolution of the galaxy population from that particular period, the so-called "Cosmic Noon", to the present epoch. The main topics addressed are the contribution of emission lines to the optical light of galaxies through cosmic time, the star formation rates of actively star-forming galaxies and quenched galaxies, and the evolution of the stellar ages of galaxies from 10 billion years ago to the current time. Show less
The question of how the first stars formed and assembled into galaxies lies at the frontier of modern astrophysics. The study of these first sources of cosmic illumination was transformed by the... Show moreThe question of how the first stars formed and assembled into galaxies lies at the frontier of modern astrophysics. The study of these first sources of cosmic illumination was transformed by the installation of new instrumentation aboard the Hubble Space Telescope during one of the final Space Shuttle missions in 2009. Hubble has since unveiled a population of ultra-faint galaxies seen just a few hundred million years after the Big Bang, an epoch often termed the Cosmic Dawn. This thesis presents pioneering observational studies of the first generations of galaxies, enabling an examination of their properties and the physics that governed the illumination of the early cosmos. Show less
