Delensing galaxy surveys

Abstract

Weak gravitational lensing can cause displacements, magnification, rotation and shearing of the images of distant galaxies. Most studies focus on the shear and magnification effects since they are more easily observed. In this paper, we focus on the effect of lensing displacements on wide field images. Galaxies at redshifts 0.5-1 are typically displaced by 1 arcmin, and the displacements are coherent over degree-sized patches. However, the displacement effect is redshift dependent, so there is a visible relative shift between galaxies at different redshifts, even if they are close on the sky.We show that the reconstruction of the original galaxy position is now feasible with lensing surveys that cover many hundreds of square degrees.We test with simulations two approaches to 'delensing': one uses shear measurements and the other uses the foreground galaxy distribution as a proxy for the mass. We also estimate the effect of foreground deflections on galaxy-galaxy lensing measurements and find it is relevant only for the Large Synoptics Survey Telescope and Euclid-era surveys. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.