Abstract
Weak lensing by largescale structure is a powerful probe of cosmology and of the dark universe. This cosmic shear technique relies on the accurate measurement of the shapes and redshifts of background galaxies and requires precise control of systematic errors. Monte Carlo control loops (MCCL) is a forward modeling method designed to tackle this problem. It relies on the ultra fast image generator (UFig) to produce simulated images tuned to match the target data statistically, followed by calibrations and tolerance loops. We present the first endtoend application of this method, on the Dark Energy Survey (DES) Year 1 wide field imaging data. We simultaneously measure the shear power spectrum Cℓ and the redshift distribution n(z) of the background galaxy sample. The method includes maps of the systematic sources, point spread function (PSF), an approximate Bayesian computation (ABC) inference of the simulation model parameters, a shear calibration scheme, and a fast method to estimate the covariance matrix. We find a close statistical agreement between the simulations and the DES Y1 data using an array of diagnostics. In a nontomographic setting, we derive a set of Cℓ and n(z) curves that encode the cosmic shear measurement, as well as the systematic uncertainty. Following a blinding scheme, we measure the combination of Ωm, σ8, and intrinsic alignment amplitude A_{IA}, defined as S_{8}D_{IA }= σ_{8}(Ω_{m}/0.3)^{0.5}D_{IA}, where D_{IA} = 1 − 0.11(A_{IA}−1). We find S_{8}D_{IA }= 0.895+0.054−0.039, where systematics are at the level of roughly 60% of the statistical errors. We discuss these results in the context of earlier cosmic shear analyses of the DES Y1 data. Our findings indicate that this method and its fast runtime offer good prospects for cosmic shear measurements with future widefield surveys.
Original language  English 

Article number  082003 
Number of pages  29 
Journal  Physical Review D  Particles, Fields, Gravitation and Cosmology 
Volume  101 
Issue number  8 
Early online date  15 Apr 2020 
DOIs  
Publication status  Published  27 Apr 2020 
Keywords
 astroph.CO
 RCUK
 STFC
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Data availability statement for 'Monte Carlo control loops for cosmic shear cosmology with DES Year 1 data'.
Amara, A. (Creator) & Avila Perez, S. (Creator), American Physical Society, 15 Apr 2020
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