Constraining cosmology using galaxy position angle-only cosmic shear

Abstract

ABSTRACT We investigate cosmological parameter inference from realistic simulated weak lensing image data using only galaxy position angles, as opposed to full-ellipticity information. We demonstrate that input shear fields can be accurately reconstructed using only the statistics of source galaxy position angles and that, from these shear fields, we can successfully recover power spectra and infer the input cosmology. This paper builds on previous work on angle-only weak lensing estimation by extending the method to deal with variable and anisotropic point spread function (PSF) convolution and variable shear fields. Previous work employed a weighting scheme to downweight the contribution to shear estimates from sources aligned with the PSF. This work removes the need to downweight sources by convolving them with an image of the PSF rotated by 90○. We show that this successfully undoes the rotation caused by PSF convolution, assuming we have reliable images of the PSF. We find that we can accurately recover the input shear signal from simulated weak lensing data, based loosely on current Stage III missions, using only the position angles to within an overall scale factor, and that the scale factor can be determined using a cosmology independent simulation with noise, galaxy, and PSF properties that match those of the simulated data set. We then demonstrate that we can constrain cosmological parameters using angle-only shear estimates with a constraining power comparable to a basic application of IM3SHAPE, which provides full-shape measurement information.