On cosmological bias due to the magnification of shear and position samples in modern weak lensing analyses

Abstract

ABSTRACT The magnification of galaxies in modern galaxy surveys induces additional correlations in the cosmic shear, galaxy–galaxy lensing, and clustering observables used in modern lensing ‘3 × 2 pt’ analyses, due to sample selection. In this paper, we emulate the magnification contribution to all three observables utilizing the SLICS simulations suite, and test the sensitivity of the cosmological model, galaxy bias, and redshift distribution calibration to un-modelled magnification in a Stage-IV-like survey using Monte Carlo sampling. We find that magnification cannot be ignored in any single or combined observable, with magnification inducing >1σ biases in the w0−σ8 plane, including for cosmic shear and 3 × 2 pt analyses. Significant cosmological biases exist in the 3 × 2 pt and cosmic shear from magnification of the shear sample alone. We show that magnification induces significant biases in the mean of the redshift distribution where a position sample is analysed, which may potentially be used to identify contamination by magnification.