Ph.D. Candidate: Jamie McCullough
Research Advisor: Aaron Roodman & Daniel Gruen

Zoom Link: https://stanford.zoom.us/j/8117233231

Zoom Password: Email physicsstudentservices@stanford.edu for password.

The distortion of light from distant galaxies around foreground structure has key cosmological information about the nature of dark matter and dark energy. Precision cosmological inference with weak gravitational lensing is now limited by systematics and not the statistics of galaxies we observe. This thesis probes three of the largest systematics in weak lensing: (1) obtaining accurate distances to galaxies with limited photometric data, photo-zs, (2) understanding how galaxy shapes intrinsically correlate with one another, intrinsic alignment (IA), and (3) estimating the response of a galaxy's shape to gravitational shear, or shear bias. This thesis discusses my work in understanding and mitigating these systematics within the Dark Energy Survey (DES) Year 3 analysis. I further outline two optical spectroscopic redshift programs with the Dark Energy Spectroscopic Instrument (DESI) and the 4-metre Multi-Object Spectroscopic Telescope (4MOST) that work to inform the color-redshift relation for distant galaxies. Lastly, I describe the results of a new cosmic shear analysis with DES Y3 that selects on blue, star-forming galaxies to diminish the impact of uncertain intrinsic alignment –  a  choice that substantially reduces tensions with early universe probes in the measured amplitude of the matter fluctuation spectrum, S8, and provides a promising avenue for next generation, Stage IV lensing surveys.