KiDS-1000: Cosmic shear with enhanced redshift calibration

We present a cosmic shear analysis with an improved redshift calibration for the fourth data release of the Kilo-Degree Survey (KiDS-1000) using self-organising maps (SOMs). Compared to the previous analysis of the KiDS-1000 data, we expand the redshift calibration sample to more than twice its size, now consisting of data of 17 spectroscopic redshift campaigns, and significantly extending the fraction of KiDS galaxies we are able to calibrate with our SOM redshift methodology. We then enhanced the calibration sample with precision photometric redshifts from COSMOS2015 and the Physics of the Accelerated Universe Survey (PAUS), allowing us to fill gaps in the spectroscopic coverage of the KiDS data. Finally we performed a Complete Orthogonal Sets of E/B-Integrals (COSEBIs) cosmic shear analysis of the newly calibrated KiDS sample. We found S (8) = 0.748(-)(0.)(025)(+0.021) which is in good agreement with previous KiDS studies and increases the tension with measurements of the cosmic microwave background to 3.4 sigma. We repeated the redshift calibration with different subsets of the full calibration sample and obtained, in all cases, agreement within at most 0.5 sigma - in S (8) compared to our fiducial analysis. Including additional photometric redshifts allowed us to calibrate an additional 6% of the source galaxy sample. Even though further systematic testing with simulated data is necessary to quantify the impact of redshift outliers, precision photometric redshifts can be beneficial at high redshifts and to mitigate selection effects commonly found in spectroscopically selected calibration samples.

Automated summary

In this study, a cosmic shear analysis with an improved redshift calibration for the fourth data release of the Kilo-Degree Survey (KiDS-1000) was presented using self-organising maps (SOMs). The redshift calibration sample was expanded to include data from 17 spectroscopic redshift campaigns and was enhanced with precision photometric redshifts from COSMOS2015 and the Physics of the Accelerated Universe Survey (PAUS). A Complete Orthogonal Sets of E/B-Integrals (COSEBIs) cosmic shear analysis was performed on the newly calibrated KiDS sample. The results showed good agreement with previous studies and increased the tension with measurements of the cosmic microwave background.