Toward understanding the anisotropic point spread function of Suprime-Cam and its impact on cosmic shear measurement

TL;DR

This study analyzes the anisotropic PSF of Suprime-Cam, decomposing its components, modeling optical aberrations, and assessing their impact on cosmic shear measurements, highlighting correction methods and residual systematics.

Contribution

It provides a detailed empirical decomposition of PSF anisotropies into optical, atmospheric, and misalignment components, and evaluates their effects on cosmic shear analysis.

Findings

Optical aberration dominates PSF ellipticity in long exposures.

Optical PSF can be corrected with polynomial fitting.

Residual PSF anisotropies are consistent with observed B-mode shear variance.

Abstract

We examined the anisotropic point spread function (PSF) of Suprime-Cam data utilizing dense star field data. We decomposed the PSF ellipticities into three components, the optical aberration, atmospheric turbulence, and chip-misalignment in an empirical manner, and evaluated the amplitude of each component. We found that, for long-exposure data, the optical aberration has the largest contribution to the PSF ellipticities, which could be modeled well by a simple analytic function based on the lowest-order aberration theory. The statistical properties of PSF ellipticities resulting from the atmospheric turbulence were investigated by using the numerical simulations. The simulation results are in a reasonable agreement with the observed data. It is also found that the optical PSF can be well corrected by the standard correction method with a polynomial fitting function. However, for the atmospheric PSF, its correction is affected by the common limitation caused by sparse sampling of PSFs due to a limited number of stars. We also examined the effects of the residual PSF anisotropies on Suprime-Cam cosmic shear data. We found that the shape and amplitude of the B-mode shear variance are broadly consistent with those of the residual PSF ellipticities measured from the dense star field data. This indicates that most of the sources of residual systematic are understood, which is an important step for cosmic shear statistics to be a practical tool of the precision cosmology.