Constraining cosmology using galaxy position angle-only cosmic shear

TL;DR

This paper demonstrates that galaxy position angles alone can be used to accurately reconstruct shear fields and infer cosmological parameters, offering a viable alternative to traditional ellipticity-based weak lensing methods.

Contribution

The authors extend angle-only weak lensing methods to handle variable PSF and shear fields, removing the need for downweighting sources and achieving comparable cosmological constraints.

Findings

Accurate shear reconstruction from position angles in simulated data.

Successful recovery of input shear signals with a known scale factor.

Cosmological parameter constraints comparable to full-ellipticity methods.

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 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 $90^{\circ}$. We show thats 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 a simulated Stage III-like weak lensing data set 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 the observed data set. We then demonstrate that we can constrain cosmological parameters using angle-only shear estimates with a constraining power comparable to using current state-of-the-art shape measurement techniques that provide full-ellipticity information.