Mitigating the effects of undersampling in weak lensing shear estimation
  with metacalibration
  Metacalibration is a state-of-the-art technique for measuring weak
gravitational lensing shear from well-sampled galaxy images. We investigate the
accuracy of shear measured with metacalibration from fitting elliptical
Gaussians to undersampled galaxy images. In this case, metacalibration
introduces aliasing effects leading to an ensemble multiplicative shear bias
about 0.01 for Euclid, and even larger for the Roman Space Telescope, well
exceeding the missions' requirements. We find that this aliasing bias can be
mitigated by computing shapes from weighted moments with wider Gaussians as
weight functions, thereby trading bias for a slight increase in variance of the
measurements. We show that this approach is robust to the point-spread function
in consideration and meets the stringent requirements of Euclid for galaxies
with moderate to high signal-to-noise ratios. We therefore advocate
metacalibration as a viable shear measurement option for weak lensing from
upcoming space missions.
