Systematic Biases In Weak Lensing Cosmology With The Dark Energy Survey release_nhm747tbx5buzdxqgx66reyoxq

by Simon Samuroff, Sarah Bridle

Published by Zenodo.

2019  

Abstract

PhD thesis submitted to the University of Manchester, School of Physics and Astronomy, August 2017. Abstract: This thesis presents a practical guide to applying shear measurements as a cosmological tool. <br> We first present one of two science-ready galaxy shape catalogues from Year 1 of the Dark Energy Survey (DES Y1), which covers 1500 square degrees in four bands griz, with a median redshift of 0.59. We describe the shape measurement process implemented by the DES Y1 im3shape catalogue, which contains 21.9M high-quality r-band bulge/disc fits. In Chapter 3 a new suite of image simulations, referred to as hoopoe, are presented. The hoopoe dataset is tailored to DES Y1 and includes realistic blending, spatial masks and variation in the point spread function. We derive shear corrections, which we show are robust to changes in calibration method, galaxy binning and variance within the simulated dataset. Sources of systematic uncertainty in the simulation-based shear calibration are discussed, leading to a final estimate of the 1 sigma uncertainties in the residual multiplicative bias after calibration of 0.025. Chapter 4 describes an extension of the analysis on the hoopoe simulations into<br> a detailed investigation of the impact of galaxy neighbours on shape measurement and shear cosmology. Four mechanisms by which neighbours can have a non-negligible influence on shear measurement are identified. These effects, if ignored, would contribute a net multiplicative bias of m ~ 0.03 - 0.09 in DES Y1, though the precise impact will depend on both the measurement code and the selection cuts applied. We use the cosmological inference pipeline of DES Y1 to explore the cosmological implications of neighbour bias and show that omitting blending from the calibration simulation for DES Y1 would bias the inferred clustering amplitude S8 = sigma_8 (Omega_m /0.3)^0.5 by 1.5 sigma towards low values. Finally, we use the hoopoe simulations to test the effect of neighbour-induced spatial correlations in the multiplicative bi [...]
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