Euclid: The reduced shear approximation and magnification bias for Stage IV cosmic shear experiments
Abstract
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. In this work, we evaluate the impact of the reduced shear approximation and magnification bias, on the 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. 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. These effects cause significant biases in Omega_m, sigma_8, n_s, Omega_DE, w_0, and w_a of -0.53 sigma, 0.43 sigma, -0.34 sigma, 1.36 sigma, -0.68 sigma, and 1.21 sigma, respectively. We then show that these lensing biases interact with another systematic: the intrinsic alignment of galaxies. Accordingly, we develop 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.
Keywords
Cite
@article{arxiv.1912.07326,
title = {Euclid: The reduced shear approximation and magnification bias for Stage IV cosmic shear experiments},
author = {A. C. Deshpande and T. D. Kitching and V. F. Cardone and P. L. Taylor and S. Casas and S. Camera and C. Carbone and M. Kilbinger and V. Pettorino and Z. Sakr and D. Sapone and I. Tutusaus and N. Auricchio and C. Bodendorf and D. Bonino and M. Brescia and V. Capobianco and J. Carretero and M. Castellano and S. Cavuoti and R. Cledassou and G. Congedo and L. Conversi and L. Corcione and M. Cropper and F. Dubath and S. Dusini and G. Fabbian and E. Franceschi and M. Fumana and B. Garilli and F. Grupp and H. Hoekstra and F. Hormuth and H. Israel and K. Jahnke and S. Kermiche and B. Kubik and M. Kunz and F. Lacasa and S. Ligori and P. B. Lilje and I. Lloro and E. Maiorano and O. Marggraf and R. Massey and S. Mei and M. Meneghetti and G. Meylan and L. Moscardini and C. Padilla and S. Paltani and F. Pasian and S. Pires and G. Polenta and M. Poncet and F. Raison and J. Rhodes and M. Roncarelli and R. Saglia and P. Schneider and A. Secroun and S. Serrano and G. Sirri and J. L. Starck and F. Sureau and A. N. Taylor and I. Tereno and R. Toledo-Moreo and L. Valenziano and Y. Wang and J. Zoubian},
journal= {arXiv preprint arXiv:1912.07326},
year = {2020}
}
Comments
16 pages, 6 figures, submitted to Astronomy & Astrophysics on 16/12/2019, accepted on 04/03/2020. SSC Fisher procedure corrected