# KiDS+VIKING-450: Cosmic shear tomography with optical+infrared data

## TL;DR

This study performs a cosmic shear analysis combining optical and near-infrared data over 450 square degrees, improving redshift estimates and confirming the persistent tension with Planck CMB measurements.

## Contribution

First to use a full optical to near-infrared dataset for wide-field cosmic shear, enhancing redshift accuracy and systematic control in weak lensing analysis.

## Key findings

- Measured $S_8=0.737_{-0.036}^{+0.040}$, consistent with previous KiDS results.
- Confirmed the 2.3 sigma tension with Planck CMB measurements.
- Systematic errors are under control with no significant B-modes detected.

## Abstract

We present a tomographic cosmic shear analysis of the Kilo-Degree Survey (KiDS) combined with the VISTA Kilo-Degree Infrared Galaxy Survey (VIKING). This is the first time that a full optical to near-infrared data set has been used for a wide-field cosmological weak lensing experiment. This unprecedented data, spanning $450~$deg$^2$, allows us to improve significantly the estimation of photometric redshifts, such that we are able to include robustly higher-redshift sources for the lensing measurement, and - most importantly - solidify our knowledge of the redshift distributions of the sources. Based on a flat $\Lambda$CDM model we find $S_8\equiv\sigma_8\sqrt{\Omega_{\rm m}/0.3}=0.737_{-0.036}^{+0.040}$ in a blind analysis from cosmic shear alone. The tension between KiDS cosmic shear and the Planck-Legacy CMB measurements remains in this systematically more robust analysis, with $S_8$ differing by $2.3\sigma$. This result is insensitive to changes in the priors on nuisance parameters for intrinsic alignment, baryon feedback, and neutrino mass. KiDS shear measurements are calibrated with a new, more realistic set of image simulations and no significant B-modes are detected in the survey, indicating that systematic errors are under control. When calibrating our redshift distributions by assuming the 30-band COSMOS-2015 photometric redshifts are correct (following the Dark Energy Survey and the Hyper Suprime-Cam Survey), we find the tension with Planck is alleviated. The robust determination of source redshift distributions remains one of the most challenging aspects for future cosmic shear surveys.