Thesis Defense: Patrick Kelly

Abstract: Observations of supernova (SN) explosions and galaxy clusters have been essential to the construction of the standard Λ-CDM cosmological model. Type Ia SN are powerful probes of the cosmic expansion history and were the tools used to discover cosmic acceleration more than a decade ago. They are the thermonuclear explosions of white dwarf stars, and regular patterns in their light curves and luminosities enable distance measurements with a precision of ∼10%. Core-collapse SN, which signal instead the deaths of young, massive stars, also have use as cosmological distance indicators and can be detected, when accompanied by a GRB, to very high redshift. A very different technique for constraining cosmological parameters is to measure the distribution of galaxy clusters as a function of mass and redshift within well-defined X-ray or optical surveys. For this method, the current limiting systematic uncertainty is the calibration of galaxy-cluster mass proxies such as total X-ray luminosity or cluster richness.

In this thesis, I discuss the discovery that SNe Ia found in more massive host galaxies are ∼10% brighter, after light curve corrections for stretch and color, than those in less massive galaxies. I also demonstrate the existence of strong patterns among the explosion environments of core-collapse SN which point to the effects of progenitor age and metallicity on massive stellar evolution. Finally, I present a weak-lensing mass analysis of 51 X-ray–luminous galaxy clusters. The inclusion of these lensing mass estimates in current cosmological analyses will improve significantly the calibration of X-ray mass proxies and increase both the accuracy and precision of galaxy cluster cosmological constraints.