Enabling Galaxy Clustering and Dynamics as Tools of Precision Cosmology

Abstract

In the era of large-area surveys, cosmology has seen enormous growth in the amount of available data and a corresponding decrease in the statistical uncertainty of measurements made with this data. The increased precision has led to the discovery of differences between measurements based on the local versus early Universe. One of the most notable differences is a 4.4? tension between the expansion rate of the Universe measured directly with Type Ia supernovae versus that inferred from measurements of the Cosmic Microwave Background (CMB). This tension could be an exciting indication of new physics or a result of unknown systematic uncertainties becoming increasingly important as the statistical uncertainty decreases. In this dissertation, I first explore the possibility of systematic uncertainties due to various observing conditions, such as sky brightness and exposure time. Variations in these conditions lead to variations in the observed density of galaxies, which are difficult to differentiate from variations sourced by cosmology. I introduce a novel method for mitigating the impact of these observing conditions and correctly propagates the uncertainty due to the mitigation into the resulting cosmological analysis. I apply the method to Year 1 (Y1) data from the Dark Energy Survey (DES) and compare the results to the fiducial DES Y1 analysis. I find that this new method results in a modest improvement in the goodness of fit for the recovered cosmological parameters (Δx2 = -6.5 with no additional parameters). Second, I propose a new method for measuring the distance-redshift relation that is independent of both the distance ladder and the theoretical systematics of CMB measurements. I show that such a method is already feasible with existing data, and I forecast the constraining power of this measurement withnear-future data from the Dark Energy Spectroscopic Instrument (DESI). Without any added information, this method applied to DESI data will result in a ~1.3% measurement of the expansion rate. Adding cosmological supernova data improves the constraint to ~0.7%. This level of precision is enough to distinguish between local measurements of the expansion rate and those based on the CMB at high confidence.