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

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 $0.8\ddot{I}ƒ$ reduction in the DES-inferred value for $S_8$, which decreases to a $0.5\ddot{I}ƒ$ 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 $S_8=0.762_{-0.024}^{+0.025}$ is in tension with the Planck 2018 constraint from the cosmic microwave background at the level of $2.5\ddot{I}ƒ$. This result highlights the importance of developing methods to provide accurate redshift calibration for current and future weak lensing surveys.

8 pages, 4 figures, new appendix added including a simulated analysis, version accepted for publication by A&A Letters, chains can be found at https://github.com/sjoudaki/kidsdes