Seeing in the dark -- I. Multi-epoch alchemy
Eric M. Huff, Christopher M. Hirata, Rachel Mandelbaum, David, Schlegel, Uros Seljak, Robert H. Lupton

TL;DR
This paper demonstrates that existing analysis techniques can effectively correct PSF effects in ground-based weak lensing surveys, enabling reliable cosmic shear measurements despite atmospheric and instrumental distortions.
Contribution
It introduces a method combining co-added SDSS imaging and a rounding kernel to null out PSF anisotropies, addressing a key systematic in weak lensing analysis.
Findings
PSF correction reduces spurious shear to negligible levels
Identifies a new systematic bias from masking in shear auto-correlations
Discusses conditions for applying this method to future surveys
Abstract
Weak lensing by large-scale structure is an invaluable cosmological tool given that most of the energy density of the concordance cosmology is invisible. Several large ground-based imaging surveys will attempt to measure this effect over the coming decade, but reliable control of the spurious lensing signal introduced by atmospheric turbulence and telescope optics remains a challenging problem. We address this challenge with a demonstration that point-spread function (PSF) effects on measured galaxy shapes in current ground-based surveys can be corrected with existing analysis techniques. In this work, we co-add existing Sloan Digital Sky Survey imaging on the equatorial stripe in order to build a data set with the statistical power to measure cosmic shear, while using a rounding kernel method to null out the effects of the anisotropic PSF. We build a galaxy catalogue from the combined…
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