Revisiting CFHTLenS cosmic shear: Optimal E/B mode decomposition using COSEBIs and compressed COSEBIs

TL;DR

This paper re-analyzes the CFHTLenS weak lensing data using COSEBIs for optimal E/B mode separation, revealing previously undetected B-modes on large scales and introducing a compressed COSEBIs method for better cosmological parameter sensitivity.

Contribution

It introduces a compressed COSEBIs approach for efficient analysis of weak lensing data, improving systematic error detection and parameter estimation.

Findings

Significant B-modes detected on large scales with standard analysis.

Tomographic analysis enhances B-mode significance, indicating potential systematics.

Compressed COSEBIs yield B-modes consistent with zero across scales.

Abstract

We present a re-analysis of the CFHTLenS weak gravitational lensing survey using Complete Orthogonal Sets of E/B-mode Integrals, known as COSEBIs. COSEBIs provide a complete set of functions to efficiently separate E-modes from B-modes and hence allow for robust and stringent tests for systematic errors in the data. This analysis reveals significant B-modes on large angular scales that were not previously seen using the standard E/B decomposition analyses. We find that the significance of the B-modes is enhanced when the data is split by galaxy type and analysed in tomographic redshift bins. Adding tomographic bins to the analysis increases the number of COSEBIs modes, which results in a less accurate estimation of the covariance matrix from a set of simulations. We therefore also present the first compressed COSEBIs analysis of survey data, where the COSEBIs modes are optimally combined based on their sensitivity to cosmological parameters. In this tomographic CCOSEBIs analysis we find the B-modes to be consistent with zero when the full range of angular scales are considered.