Query : 2011A&A...536A..85H

2011A&A...536A..85H - Astronomy and Astrophysics, volume 536A, 85-85 (2011/12-1)

Cosmic shear covariance: the log-normal approximation.


Abstract (from CDS):

Accurate estimates of the errors on the cosmological parameters inferred from cosmic shear surveys require accurate estimates of the covariance of the cosmic shear correlation functions. We seek approximations to the cosmic shear covariance that are as easy to use as the common approximations based on normal (Gaussian) statistics, but yield more accurate covariance matrices and parameter errors. We derive expressions for the cosmic shear covariance under the assumption that the underlying convergence field follows log-normal statistics. We also derive a simplified version of this log-normal approximation by only retaining the most important terms beyond normal statistics. We use numerical simulations of weak lensing to study how well the normal, log-normal, and simplified log-normal approximations as well as empirical corrections to the normal approximation proposed in the literature reproduce shear covariances for cosmic shear surveys. We also investigate the resulting confidence regions for cosmological parameters inferred from such surveys. We find that the normal approximation substantially underestimates the cosmic shear covariances and the inferred parameter confidence regions, in particular for surveys with small fields of view and large galaxy densities, but also for very wide surveys. In contrast, the log-normal approximation yields more realistic covariances and confidence regions, but also requires evaluating slightly more complicated expressions. However, the simplified log-normal approximation, although as simple as the normal approximation, yields confidence regions that are almost as accurate as those obtained from the log-normal approximation. The empirical corrections to the normal approximation do not yield more accurate covariances and confidence regions than the (simplified) log-normal approximation. Moreover, they fail to produce positive-semidefinite data covariance matrices in certain cases, rendering them unusable for parameter estimation. The log-normal or simplified log-normal approximation should be used in favour of the normal approximation for parameter estimation and parameter error forecasts. More generally, any approximation to the cosmic shear covariance should ensure a positive-(semi)definite data covariance matrix.

Abstract Copyright:

Journal keyword(s): methods: numerical - large-scale structure of Universe - cosmological parameters - gravitational lensing: weak - cosmology: theory - methods: analytical

Simbad objects: 2

goto Full paper

goto View the references in ADS

Number of rows : 2
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
1 NAME Chandra Deep Field-South reg 03 32 28.0 -27 48 30           ~ 2045 1
2 NAME COSMOS Field reg 10 00 28.60 +02 12 21.0           ~ 2822 0

To bookmark this query, right click on this link: simbad:objects in 2011A&A...536A..85H and select 'bookmark this link' or equivalent in the popup menu


© Université de Strasbourg/CNRS

    • Contact