Lunch talk on Sep. 21, 2026

Precision Measurement of Large Shear Signals

Speaker: Jiarui Sun (Shanghai Jiao Tong University)

Venue: SWIFAR Building 2111

Time: 12:45 PM, Monday, Sep. 21, 2026

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 the point spread function (PSF) and noise. In this work, we propose a non-perturbative method to exactly recover large shear signals ($\gtrsim 0.5$) under general conditions.  Tests on simulated galaxy images demonstrate that the method remains accurate even for very faint sources. We further apply the method to James Webb Space Telescope (JWST) observations of the galaxy cluster Abell 2744, reconstructing its projected mass distribution and constraining the parameters of a Navarro–Frenk–White (NFW) halo model. This method enables more accurate mapping of shear around massive foreground clusters and improved characterization of their underlying dark matter halos.