Abstract

Weak lensing surveys estimate the clustering of matter in the Universe by measuring the correlations in galaxy shapes. These surveys are powerful tools for constraining cosmological model parameters in the nearby Universe. However, most weak lensing surveys estimate the matter clumpiness (S8) to be lower than the value derived from Planck cosmic microwave background (CMB) observations. A better understanding of this difference is crucial, as it may point to new physics. An accurate weak lensing analysis is becoming more challenging as we increase statistical power by upscaling survey observations. One of the key steps in the weak lensing analysis is the ‘shear’ estimation, which quantifies the apparent change in galaxy ellipticities due to lensing. Within the Kilo-Degree Survey (KiDS) team, we recently developed a new shear estimation pipeline, based on MetaCalibration, to complement the existing fiducial pipeline (Lensfit). Performance tests demonstrate that MetaCalibration is robust and less dependent on the fidelity of the image simulations. Using this new pipeline, we derive revised cosmological constraints for KiDS. Furthermore, both KiDS shear pipelines are now being implemented in Euclid, enabling robust weak lensing analyses and facilitating scientific breakthroughs by observing billions of galaxies.