Lensing Systematics from Space: Modeling PSF effects in the SNAP survey

TL;DR

This paper models the PSF anisotropy effects in the SNAP space telescope, quantifies their impact on weak lensing measurements, and finds that these systematics are smaller than the statistical errors expected.

Contribution

It provides a detailed simulation of PSF systematics in space-based weak lensing surveys, highlighting the dominant thermal drift effect and its relative insignificance compared to statistical errors.

Findings

Thermal drift is the dominant PSF systematic effect.

PSF systematics are smaller than the expected statistical errors.

Time-varying PSFs contribute at a level manageable for weak lensing analysis.

Abstract

Anisotropy in the point spread function (PSF) contributes a systematic error to weak lensing measurements. In this study we use a ray tracer that incorporates all the optical elements of the SNAP telescope to estimate this effect. Misalignments in the optics generates PSF anisotropy, which we characterize by its ellipticity. The effect of three time varying effects: thermal drift, guider jitter, and structural vibration on the PSF are estimated for expected parameters of the SNAP telescope. Multiple realizations of a thousand square degree mock survey are then generated to include the systematic error pattern induced by these effects. We quantify their contribution to the power spectrum of the lensing shear. We find that the dominant effect comes from the thermal drift, which peaks at angular wavenumbers l ~ 10^3, but its amplitude is over one order of magnitude smaller than the size of the expected statistical error. While there are significant uncertainties in our modeling, our study indicates that time-varying PSFs will contribute at a smaller level than statistical errors in SNAP's weak lensing measurements.