Toward Understanding the Anisotropic Point Spread Function of Suprime-Cam and Its Impact on Cosmic Shear Measurement

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 then tested a standard method for correcting the PSF ellipticities used in weak lensing analysis against a mock simulation. 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 atmospheric turbulence were investigated by using numerical simulations. The simulation results are in a reasonable agreement with the observed data. It follows from these findings that the spatial variation of PSF ellipticities consists of two components: one is a smooth and parametrizable component arising from the optical PSF, and the other is a non-smooth and stochastic component resulting from the atmospheric PSF. The former can be well corrected by the standard correction method with a polynomial fitting function. However, for the latter, 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 (5.6-degree2 of i′-band 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.