Emulating redshift mixing due to blending in weak gravitational lensing

Astronomy and Astrophysics, vol. 706, pp. A234

Abstract

Context. Galaxies whose images overlap in the focal plane of a telescope, commonly referred to as blends, are often located at different redshifts. Blending introduces a challenge to weak-lensing cosmology probes since such blends are subject to shear signals from multiple redshifts. Aims. This effect can be described by joining shear bias and redshift characterisation in the effective redshift distribution, n γ ( z ), which includes the response of apparent shapes of detected objects to shear of galaxies at redshift, z . In this work, we propose a novel method to correct n γ ( z ) for redshift-mixed blending by emulating the shear response to neighbouring galaxies. Methods. We designed a ‘half-sky-shearing’ simulation with Subaru Hyper Suprime Cam (HSC) wide-like specifications, which allowed us to extract the response of a detected object’s measured ellipticity to the shearing of neighbouring galaxies among numerous galaxy pairs. Results. We demonstrate the feasibility of accurately emulating these pairwise responses and validate the robustness of our approach under varying observing conditions and galaxy population uncertainties. We find that the effective redshift of sources at the high-redshift tail of the distribution is about 0.05 lower than expected when the effect is not modelled. Conclusions. Given adequately processed image simulations, our correction method can be readily incorporated into future cosmological analyses to mitigate this source of systematic error.

Authors 5

1. Zekang Zhang

   Ludwig-Maximilians-Universität München

   Affiliation as printed

   Universitäts-Sternwarte, Fakultät für Physik, Ludwig-Maximilians Universität München

2. Daniel Gruen

   Excellence Cluster Origins · Ludwig-Maximilians-Universität München

   Affiliation as printed

   Excellence Cluster ORIGINS

   Universitäts-Sternwarte, Fakultät für Physik, Ludwig-Maximilians Universität München

3. Luca Tortorelli

   Ludwig-Maximilians-Universität München

   Affiliation as printed

   Universitäts-Sternwarte, Fakultät für Physik, Ludwig-Maximilians Universität München

4. Shangrong Li Aachen Leiden Observatory

   Leiden University · Leiden Observatory · Ruhr University Bochum

   Affiliation as printed

   Leiden Observatory, Leiden University

   Ruhr University Bochum, Faculty of Physics and Astronomy, Astronomical Institute (AIRUB), German Centre for Cosmological Lensing

5. J. McCullough

   Princeton University

   Affiliation as printed

   Department of Astrophysical Sciences, Princeton University