# KiDS+VIKING-450 and DES-Y1 combined: Cosmology with cosmic shear

## TL;DR

This paper combines weak gravitational lensing data from KV450 and DES-Y1 to refine cosmological parameters, emphasizing the importance of accurate redshift calibration and revealing a tension with Planck 2018 results.

## Contribution

It presents a homogenized analysis of two major cosmic shear datasets with revised redshift distributions, improving parameter constraints and highlighting calibration challenges.

## Key findings

- Combined constraint on S8: 0.762^{+0.025}_{-0.024}
- Redshift revisions reduce S8 tension with Planck from 2.5σ to 0.5σ
- Emphasizes need for precise redshift calibration in weak lensing surveys.

## Abstract

We present a combined tomographic weak gravitational lensing analysis of the Kilo Degree Survey (KV450) and the Dark Energy Survey (DES-Y1). We homogenize the analysis of these two public cosmic shear datasets by adopting consistent priors and modeling of nonlinear scales, and determine new redshift distributions for DES-Y1 based on deep public spectroscopic surveys. Adopting these revised redshifts results in a $0.8\sigma$ reduction in the DES-inferred value for $S_8$, which decreases to a $0.5\sigma$ reduction when including a systematic redshift calibration error model from mock DES data based on the MICE2 simulation. The combined KV450 + DES-Y1 constraint on $S_8 = 0.762^{+0.025}_{-0.024}$ is in tension with the Planck 2018 constraint from the cosmic microwave background at the level of $2.5\sigma$. This result highlights the importance of developing methods to provide accurate redshift calibration for current and future weak lensing surveys.