Accurate cosmic shear errors: do we need ensembles of simulations?
Abstract
Accurate inference of cosmology from weak lensing shear requires an accurate shear power spectrum covariance matrix. Here, we investigate this accuracy requirement and quantify the relative importance of the Gaussian (G), supersample covariance (SSC) and connected nonGaussian (cNG) contributions to the covariance. Specifically, we forecast cosmological parameter constraints for future widefield surveys and study how different covariance matrix components affect parameter bounds. Our main result is that the cNG term represents only a small and potentially negligible contribution to statistical parameter errors: the errors obtained using the G+SSC subset are within lesssim 5% of those obtained with the full G+SSC+cNG matrix for a Euclidlike survey. This result also holds for the shear twopoint correlation function, variations in survey specifications and for different analytical prescriptions of the cNG term. The cNG term is that which is often tackled using numerically expensive ensembles of survey realizations. Our results suggest however that the accuracy of analytical or approximate numerical methods to compute the cNG term is likely to be sufficient for cosmic shear inference from the next generation of surveys.
 Publication:

Journal of Cosmology and Astroparticle Physics
 Pub Date:
 October 2018
 DOI:
 10.1088/14757516/2018/10/053
 arXiv:
 arXiv:1807.04266
 Bibcode:
 2018JCAP...10..053B
 Keywords:

 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 15 pages, 5 figures, 1 table. Comments welcomed. Changes in v2: (i) improved visualization of Fig.1