Delensing Galaxy Surveys
  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 arcminute, and the displacements
are coherent over degree-size 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 LSST and Euclid-era surveys.
