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), estimated using redshift distributions and photometric
samples defined using self-organising maps (SOMs). Our fiducial analysis finds
marginal posterior constraints of $S_8\equiv\sigma_8\sqrt{\Omega_{\rm
m}/0.3}=0.716^{+0.043}_{-0.038}$; smaller than, but otherwise consistent with,
previous work using this data set ($|\Delta S_8| = 0.023$). We analyse
additional samples and redshift distributions constructed in three ways:
excluding certain spectroscopic surveys during redshift calibration, excluding
lower-confidence spectroscopic redshifts in redshift calibration, and
considering only photometric sources which are jointly calibrated by at least
three spectroscopic surveys. In all cases, the method utilised here proves
robust: we find a maximal deviation from our fiducial analysis of $|\Delta S_8|
\leq 0.011$ for all samples defined and analysed using our SOM. To demonstrate
the reduction in systematic biases found within our analysis, we highlight our
results when performing redshift calibration without the DEEP2 spectroscopic
data set. In this case we find marginal posterior constraints of
$S_8=0.707_{-0.042}^{+0.046}$; a difference with respect to the fiducial that
is both significantly smaller than, and in the opposite direction to, the
equivalent shift from previous work. These results suggest that our improved
cosmological parameter estimates are insensitive to pathological
misrepresentation of photometric sources by the spectroscopy used for direct
redshift calibration, and therefore that this systematic effect cannot be
responsible for the observed difference between $S_8$ estimates made with KV450
and Planck CMB probes.
