The SPT-3G Wide Survey Galaxy Cluster Catalog and the SPT-3G+ Cryostat Design

Measuring the evolution of the large-scale structure of the universe can probe fundamental physics, including the nature of cosmic inflation, the evolution of dark energy, and the mass of the neutrino. Galaxy clusters are the largest gravitationally bound objects in the universe and are useful probes of structure, in particular sensitive to the amplitude of matter fluctuations ($\sigma_8$) and the matter density ($\Omega_m$). Galaxy clusters are observable at millimeter wavelengths using the thermal Sunyaev-Zel'dovich (tSZ) effect due to cosmic microwave background (CMB) photons scattering off of hot electrons in the intra-cluster medium. The surface brightness of the tSZ effect is redshift independent, making it a useful probe of the evolution of structure formation out to high-redshift. In this thesis, I present a catalog of 6,870 galaxy cluster candidates selected by the tSZ effect using 5,000 square degrees of data from the South Pole Telescope's SPT-3G Wide survey, and discuss its cosmological implications. I also introduce the design of the cryostat for the next-generation SPT-3G+ camera for the South Pole Telescope (SPT), scheduled to be installed in the 2028-2029 Austral summer, which aims to significantly improve the sensitivity of SPT to find galaxy clusters. The SPT-3G+ cryostat design hosts seven modular optics tubes, each containing cryogenic silicon lenses with a metamaterial anti-reflection coating, which couples light onto detectors at 100 milliKelvin. I describe the design metrics and analytics that were used in the design of the SPT-3G+ cryostat.