Estimating the weak-lensing rotation signal in radio cosmic shear surveys

Abstract

Weak lensing has become an increasingly important tool in cosmology and the use of galaxy shapes to measure cosmic shear has become routine. The weak-lensing distortion tensor contains two other effects in addition to the two components of shear: the convergence and rotation. The rotation mode is not measurable using the standard cosmic shear estimators based on galaxy shapes, as there is no information on the original shapes of the images before they were lensed. Due to this, no estimator has been proposed for the rotation mode in cosmological weak-lensing surveys, and the rotation mode has never been constrained. Here, we derive an estimator for this quantity, which is based on the use of radio polarisation measurements of the intrinsic position angles of galaxies. The rotation mode can be sourced by physics beyond $\Lambda$CDM, and also offers the chance to perform consistency checks of $\Lambda$CDM and of weak-lensing surveys themselves. We present simulations of this estimator and show that, for the pedagogical example of cosmic string spectra, this estimator could detect a signal that is consistent with the constraints from Planck. We examine the connection between the rotation mode and the shear $B$-modes and thus how this estimator could help control systematics in future radio weak-lensing surveys.

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• KiDS+VIKING-450 and DES-Y1 combined: Mitigating baryon feedback uncertainty with COSEBIs
• KiDS-1000 Methodology: Modelling and inference for joint weak gravitational lensing and spectroscopic galaxy clustering analysis
• CMB weak-lensing beyond the Born approximation: a numerical approach
• CMB-lensing beyond the leading order: temperature and polarization anisotropies
• Cosmological gravity on all scales: simple equations, required conditions, and a framework for modified gravity
• Jacobi Mapping Approach for a Precise Cosmological Weak Lensing Formalism
• Rotation of the CMB polarisation by foreground lensing
• Dark Energy Survey Year 1: An independent E/B-mode cosmic shear analysis
• Image Rotation from weak Lensing
• Parametrizing modified gravities with vector degrees of freedom: anisotropic growth and lensing
• Testing Quadratic Maximum Likelihood estimators for forthcoming Stage-IV weak lensing surveys
• Consistent cosmological structure formation on all scales in relativistic extensions of MOND
• Testing for gravitational preferred directions with galaxy and lensing surveys