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Euclid: The reduced shear approximation and magnification bias for Stage IV cosmic shear experiments

Deshpande, AC; Kitching, TD; Cardone, VF; Taylor, PL; Casas, S; Camera, S; Carbone, C; ... Zoubian, J; + view all (2020) Euclid: The reduced shear approximation and magnification bias for Stage IV cosmic shear experiments. Astronomy & Astrophysics , 636 , Article A95. 10.1051/0004-6361/201937323. Green open access

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Abstract

Context: Stage IV weak lensing experiments will offer more than an order of magnitude leap in precision. We must therefore ensure that our analyses remain accurate in this new era. Accordingly, previously ignored systematic effects must be addressed. / Aims: In this work, we evaluate the impact of the reduced shear approximation and magnification bias on information obtained from the angular power spectrum. To first-order, the statistics of reduced shear, a combination of shear and convergence, are taken to be equal to those of shear. However, this approximation can induce a bias in the cosmological parameters that can no longer be neglected. A separate bias arises from the statistics of shear being altered by the preferential selection of galaxies and the dilution of their surface densities in high-magnification regions. / Methods: The corrections for these systematic effects take similar forms, allowing them to be treated together. We calculated the impact of neglecting these effects on the cosmological parameters that would be determined from Euclid, using cosmic shear tomography. To do so, we employed the Fisher matrix formalism, and included the impact of the super-sample covariance. We also demonstrate how the reduced shear correction can be calculated using a lognormal field forward modelling approach. / Results: These effects cause significant biases in Ωm, σ8, ns, ΩDE, w0, and wa of −0.53σ, 0.43σ, −0.34σ, 1.36σ, −0.68σ, and 1.21σ, respectively. We then show that these lensing biases interact with another systematic effect: the intrinsic alignment of galaxies. Accordingly, we have developed the formalism for an intrinsic alignment-enhanced lensing bias correction. Applying this to Euclid, we find that the additional terms introduced by this correction are sub-dominant.

Type: Article
Title: Euclid: The reduced shear approximation and magnification bias for Stage IV cosmic shear experiments
Open access status: An open access version is available from UCL Discovery
DOI: 10.1051/0004-6361/201937323
Publisher version: https://doi.org/10.1051/0004-6361/201937323
Language: English
Additional information: This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: gravitational lensing: weak / cosmology: observations / methods: analytical
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics
URI: https://discovery.ucl.ac.uk/id/eprint/10102326
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