Influence of the local Universe on weak gravitational lensing surveys
Abstract
Observations of the largescale structure (LSS) implicitly assume an ideal FriedmannLemaitreRobertsonWalker (FLRW) observer with the ambient structure having no influence on the observer. However, due to correlations in the LSS, cosmological observables are dependent on the position of an observer. We investigate this influence in full generality for a weakly nonGaussian random field, for which we derive expressions for angular spectra of LSS observables conditional on a property of the LSS that is typical for the observer's location. As an application, we then apply to the formalism to angular spectra of the weak gravitational lensing effect and provide numerical estimates for the resulting change on the spectra using linear structure formation. For angular weak lensing spectra, we find the effect to be of order of a few per cent, for instance we estimate for an overdensity of δ = 0.5 and multipoles up to ℓ = 100 the change in the weak lensing spectra to be approximately 4 per cent. We show that without accounting for correlation between the density at observer's location and the weak gravitational lensing spectra, the values of the parameters Ω_{m} and σ_{8} are underestimated by a few per cent. Thus, this effect will be important when analysing data from future surveys such as Euclid, which aim at the per centlevel precision. The effect is difficult to capture in simulations, as estimates of the number of numerical simulations necessary to quantify the effect are high.
 Publication:

Monthly Notices of the Royal Astronomical Society
 Pub Date:
 July 2019
 DOI:
 10.1093/mnras/stz944
 arXiv:
 arXiv:1812.06922
 Bibcode:
 2019MNRAS.486.5061R
 Keywords:

 gravitational lensing: weak;
 largescale structure of Universe;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 13 pages, 7 figures, figure added