KiDS+VIKING-450: Improved cosmological parameter constraints from redshift calibration with self-organising maps

We present updated cosmological constraints for the KiDS+VIKING-450 cosmic shear data set (KV450) estimatedthrough redshift distributions and photometric samples defined using self-organising maps (SOMs). Our fiducial analysisfinds marginal posterior constraints of S8≡σ8√Ωm/0.3=0.716+0.043−0.038, which are smaller but otherwise consistent withprevious works that have applied this data set (|∆S8|=0.023). We analysed additional samples and redshift distributionsset up in three ways: 1) by excluding certain spectroscopic surveys during redshift calibration; 2) by excluding lower-confidence spectroscopic redshifts in redshift calibration; and 3) by considering only those photometric sources whichare jointly calibrated by at least three spectroscopic surveys. In all cases, the method utilised here has been proven tobe robust: we find a maximal deviation from our fiducial analysis of|∆S8|≤0.011for all samples defined and analysedusing our SOM. To demonstrate the reduction in systematic biases found within our analysis, we highlight our resultswhen performing redshift calibration without the DEEP2 spectroscopic data set. In this case, we find marginal posteriorconstraints ofS8=0.707+0.046−0.042; this is a difference, with respect to the fiducial, that is both significantly smaller and inthe opposite direction with regard to the equivalent shift from previous works. These results suggest that our improvedcosmological parameter estimates are not sensitive to pathological misrepresentations of photometric sources by thespectroscopy used for direct redshift calibration and, therefore, that this systematic effect cannot be responsible for theobserved difference betweenS8estimates made with KV450 and Planck CMB probes.