Weak Gravitational Lensing Shear Estimation with Metacalibration for the Roman High-Latitude Imaging Survey

TL;DR

This study evaluates the effectiveness of the Metacalibration shear calibration method for the Roman Space Telescope's weak lensing survey using realistic simulations, highlighting current limitations and future needs for improved accuracy.

Contribution

It presents the first application of Metacalibration to realistic Roman HLIS simulations, assessing its current performance and identifying key challenges like blending effects.

Findings

Metacalibration calibrates shapes within ~0.10% in simplified simulations.

In realistic simulations, calibration accuracy drops to ~1.3%.

Results are consistent with zero bias within 1-2 sigma, limited by survey volume.

Abstract

We investigate the performance of the Metacalibration shear calibration framework using simulated imaging data for the Nancy Grace Roman Space Telescope (Roman) reference High-Latitude Imaging Survey (HLIS). The weak lensing program of the Roman mission requires the mean weak lensing shear estimate to be calibrated within about 0.03%. To reach this goal, we can test our calibration process with various simulations and ultimately isolate the sources of residual shear biases in order to improve our methods. In this work, we build on the Roman HLIS image simulation pipeline in Troxel et al. 2021 to incorporate several new realistic processing-pipeline updates necessary to more accurately process the imaging data and calibrate the shear. We show the first results of this calibration for six deg$^2$ of the simulated reference HLIS using Metacalibration and compare these results to measurements on more simple, faster Roman-like image simulations. In both cases, we neglect the impact of blending of objects. We find that in the simplified simulations, Metacalibration can calibrate shapes to be within $m=(-0.01\pm 0.10)$%. When applied to the current most-realistic version of the simulations, the precision is much lower, with estimates of $m=(-1.34\pm 0.67)$% for joint multi-band single-epoch measurements and $m=(-1.13\pm 0.60)$% for multi-band coadd measurements. These results are all consistent with zero within 1-2$\sigma$, indicating we are currently limited by our simulated survey volume. Further work on testing the shear calibration methodology is necessary at higher precision to reach the level of the Roman requirements, in particular in the presence of blending. Current results demonstrate, however, that the Metacalibration method can work on undersampled space-based Roman imaging data at levels comparable to the requirements of current weak lensing surveys.