Investigations of Star Formation and Ionizing Radiation Across Time and Spatial Scales

This thesis explores a broad range of spatial scales across a broad range of times throughout the history of the universe, with the goal of improving our understanding of star formation and the origin of ionizing radiation across these broad scales. In the nearby universe, we can examine star formation on galactic scales and at the level of individual stars. However, in the distant universe, we are often limited to only the larger galactic scales due to finite telescope resolution. However, with gravitational lensing, we can reveal similarly small scales in distant galaxies. In my work, I examined lensed galaxy substructure at redshifts z > 6 down to parsec scales, and in one case I determined that an individual star is observed at z = 6. These observations allow for detailed study of the structures of these distant galaxies, as well as the composition of a star within the first billion years of the universe. On the larger scales, galaxy clusters typically contain little active star formation. However, I examined diffuse ultraviolet radiation around massive clusters and found an excess, which could be explained by ongoing star formation in the intracluster medium. Together, these studies contribute to our understanding of star formation on multiple scales. Additionally, young, UV-bright stars are key contributors to the ionizing radiation that drove the transition from neutral to ionized hydrogen in the early universe, and contributes to continuing that ionized state today. The studies presented herein again offer a multi-scale perspective on the sources of ionizing UV light. The small scale star formation in distant galaxies can help determine how ionizing photons are created and escape from these galaxies into the intergalactic medium, where they contribute to reionization. Meanwhile, studying the UV emission from galaxy clusters provides an additional source to help make sense of the UV background light, which, at higher energies, contributes to maintaining the ionized state of the intergalactic medium