Precision Measurement of Large Shear Signals

Abstract So far, estimators of galaxy shape distortions are only carefully studied perturbatively in the case of small shear signals, mainly for weak-lensing science. However, in the neighborhood of massive foreground clusters, a large number of background galaxies can be significantly distorted. The measurement of such large shear signals could be quite nontrivial under general observing conditions, i.e., in the presence of point-spread function and noise. In this work, we propose a nonperturbative method to exactly recover large shear signals (≳0.5) under general conditions. We test the method on simulated galaxy images and find that it is accurate down to the very faint end. This new method is particularly useful for more accurate recovery of the shear distribution in the neighborhood of massive foreground clusters, thereby improving the modeling of the underlying dark matter halo properties.