Weak lensing shear calibration with simulations of the HSC survey

TL;DR

This paper develops realistic simulations incorporating HSC observing conditions and galaxy morphologies to calibrate weak lensing shear measurements, effectively controlling biases to within 1% for the HSC survey.

Contribution

The study introduces detailed simulations that include nearby galaxies and blends, improving shear calibration accuracy for the HSC survey.

Findings

Inclusion of nearby galaxies is crucial for realistic shear bias estimation.

Selection biases are identified and corrected, reducing biases to below 1%.

Shear calibration is robust against various sample cuts.

Abstract

We present results from a set of simulations designed to constrain the weak lensing shear calibration for the Hyper Suprime-Cam (HSC) survey. These simulations include HSC observing conditions and galaxy images from the Hubble Space Telescope (HST), with fully realistic galaxy morphologies and the impact of nearby galaxies included. We find that the inclusion of nearby galaxies in the images is critical to reproducing the observed distributions of galaxy sizes and magnitudes, due to the non-negligible fraction of unrecognized blends in ground-based data, even with the excellent typical seeing of the HSC survey (0.58" in the $i$-band). Using these simulations, we detect and remove the impact of selection biases due to the correlation of weights and the quantities used to define the sample (S/N and apparent size) with the lensing shear. We quantify and remove galaxy property-dependent multiplicative and additive shear biases that are intrinsic to our shear estimation method, including a $\sim 10$ per cent-level multiplicative bias due to the impact of nearby galaxies and unrecognized blends. Finally, we check the sensitivity of our shear calibration estimates to other cuts made on the simulated samples, and find that the changes in shear calibration are well within the requirements for HSC weak lensing analysis. Overall, the simulations suggest that the weak lensing multiplicative biases in the first-year HSC shear catalog are controlled at the 1 per cent level.