Weak Lensing Cosmology Analysis with Stage-III Cosmic Shear Surveys

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As light travels from distant galaxies it is coherently bent by the gravitational potential of the mass distribution between the source and the observer. This weak gravitational lensing creates correlations between galaxy shapes that can be measured as a function of redshift in a tomographic cosmic shear measurement. Cosmic shear is a powerful probe of cosmological models, as different expansion scenarios for our Universe produce different weak lensing signals as a function of redshift. Comparison of cosmic shear survey data to theoretical models is a precise test of the current standard model of cosmology; $\Lambda$CDM. The upcoming Legacy Survey of Space and Time (LSST) of the Vera C. Rubin Observatory will produce sub-percent level measurements of cosmological parameters by optically imaging billions of galaxies to unprecedented depth. In anticipation of the LSST analysis, we examine three of the most recent cosmic shear datasets: the first year data from the Dark Energy Survey (DES-Y1), the 1,000 deg$^{2}$ dataset from the Kilo-Degree Survey (KiDS-1000), and the first year data from the Hyper Suprime-Cam Subaru Strategic Program (HSC-Y1). In this work we re-analyze the cosmic shear results from each of the previous surveys using a unified pipeline from the LSST Dark Energy Science Collaboration (DESC). We then measure each of the datasets statistical consistencies, finding each of the surveys to be in agreement. We additionally assess the robustness of the results to analysis choices, and find the cosmology constraints to be robust to two different small-scale treatment methods. Finally we produce a combined cosmology constraint from the three datasets under our unified pipeline. Our combined analysis gives a $1.6-1.9\%$ constraint on the $S_{8}\equiv \sigma_{8}\sqrt{\Omega_{\rm m}/0.3}$, given different approximation methods for the cross-covariance of the overlapping HSC-Y1 and KiDS-1000 footprint. This constraint is as precise as the most recent cosmic shear survey measurement, DES-Y3. This work paves the way for a cosmology analysis with the upcoming LSST-Y1 dataset by DESC by serving as the first test of DESC pipelines on real data, and demonstrating its capabilities to reproduce Stage-III results. It additionally provides guidance to the LSST-Y1 analysis by examining the effects of prior choice and scale cuts on cosmology measurements.






Phillips Longley, Emily LaFrance (2023). Weak Lensing Cosmology Analysis with Stage-III Cosmic Shear Surveys. Dissertation, Duke University. Retrieved from https://hdl.handle.net/10161/27757.


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