Testing KiDS crosscorrelation redshifts with simulations
Abstract
Measuring cosmic shear in widefield imaging surveys requires accurate knowledge of the redshift distribution of all sources. The clusteringredshift technique exploits the angular crosscorrelation of a target galaxy sample with unknown redshifts and a reference sample with known redshifts. It represents an attractive alternative to colourbased methods of redshift calibration. Here we test the performance of such clustering redshift measurements using mock catalogues that resemble the KiloDegree Survey (KiDS). These mocks are created from the MICE simulation and closely mimic the properties of the KiDS source sample and the overlapping spectroscopic reference samples. We quantify the performance of the clustering redshifts by comparing the crosscorrelation results with the true redshift distributions in each of the five KiDS photometric redshift bins. Such a comparison to an informative model is necessary due to the incompleteness of the reference samples at high redshifts. Clustering mean redshifts are unbiased at Δz< 0.006 under these conditions. The redshift evolution of the galaxy bias of the reference and target samples represents one of the most important systematic errors when estimating clustering redshifts. It can be reliably mitigated at this level of precision using autocorrelation measurements and selfconsistency relations, and will not become a dominant source of systematic error until the arrival of StageIV cosmic shear surveys. Using redshift distributions from a direct colourbased estimate instead of the true redshift distributions as a model for comparison with the clustering redshifts increases the biases in the mean to up to Δz∼0.04. This indicates that the interpretation of clustering redshifts in realworld applications will require more sophisticated (parameterised) models of the redshift distribution in the future. If such better models are available, the clusteringredshift technique promises to be a highly complementary alternative to other methods of redshift calibration.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 October 2020
 DOI:
 10.1051/00046361/202038835
 arXiv:
 arXiv:2007.01846
 Bibcode:
 2020A&A...642A.200V
 Keywords:

 cosmology: observations;
 surveys;
 largescale structure of Universe;
 galaxies: distances and redshifts;
 Astrophysics  Cosmology and Nongalactic Astrophysics;
 Astrophysics  Instrumentation and Methods for Astrophysics
 EPrint:
 21 pages, 18 figures, 10 tables