Separating weak lensing and intrinsic alignments using radio observations

TL;DR

This paper presents novel radio observation techniques to distinguish weak gravitational lensing signals from intrinsic galaxy alignments, improving the accuracy of cosmic shear measurements.

Contribution

It introduces methods utilizing radio data, including HI emission and polarization, to separate lensing effects from intrinsic alignments in upcoming surveys.

Findings

Successfully reconstructs shear and intrinsic alignment spectra in simulations.

Biases from orientation estimate errors can be corrected with known error distributions.

Radio-based intrinsic position angles effectively reduce contamination in weak lensing analysis.

Abstract

We discuss methods for performing weak lensing using radio observations to recover information about the intrinsic structural properties of the source galaxies. Radio surveys provide unique information that can benefit weak lensing studies, such as HI emission, which may be used to construct galaxy velocity maps, and polarized synchrotron radiation; both of which provide information about the unlensed galaxy and can be used to reduce galaxy shape noise and the contribution of intrinsic alignments. Using a proxy for the intrinsic position angle of an observed galaxy, we develop techniques for cleanly separating weak gravitational lensing signals from intrinsic alignment contamination in forthcoming radio surveys. Random errors on the intrinsic orientation estimates introduce biases into the shear and intrinsic alignment estimates. However, we show that these biases can be corrected for if the error distribution is accurately known. We demonstrate our methods using simulations, where we reconstruct the shear and intrinsic alignment auto and cross-power spectra in three overlapping redshift bins. We find that the intrinsic position angle information can be used to successfully reconstruct both the lensing and intrinsic alignment power spectra with negligible residual bias.