KiDS+VIKING-450: An internal-consistency test for cosmic shear tomography with a colour-based split of source galaxies

TL;DR

This paper conducts an internal consistency check of the KiDS+VIKING-450 cosmic shear analysis by splitting source galaxies based on color, verifying calibration and nuisance parameters, and assessing residual systematics without relying on cosmological assumptions.

Contribution

It introduces a color-based split method for internal consistency testing in cosmic shear analysis and evaluates the adequacy of nuisance parameters for residual systematics.

Findings

Current nuisance parameters sufficiently capture residual systematics.

Slight deviations in redshift calibration are observed in some tomographic bins.

Degeneracy between intrinsic alignments and redshift uncertainties is identified.

Abstract

We performed an internal-consistency test of the KiDS+VIKING-450 (KV450) cosmic shear analysis with a colour-based split of source galaxies. Utilising the same measurements and calibrations for both sub-samples, we inspected the characteristics of the shear measurements and the performance of the calibration pipelines. On the modelling side, we examined the observational nuisance parameters, specifically those for the redshift calibration and intrinsic alignments, using a Bayesian analysis with dedicated test parameters. We verified that the current nuisance parameters are sufficient for the KV450 data to capture residual systematics, with slight deviations seen in the second and the third redshift tomographic bins. Our test also showcases the degeneracy between the inferred amplitude of intrinsic alignments and the redshift uncertainties in low redshift tomographic bins. The test is rather insensitive to the background cosmology and, therefore, can be implemented before any cosmological inference is made.