Testing KiDS cross-correlation redshifts with simulations

Springer Link (Chiba Institute of Technology)

Abstract

Measuring cosmic shear in wide-field imaging surveys requires accurate knowledge of the redshift distribution of all sources. The clustering-redshift technique exploits the angular cross-correlation of a target galaxy sample with unknown redshifts and a reference sample with known redshifts. It represents an attractive alternative to colour-based methods of redshift calibration. Here we test the performance of such clustering redshift measurements using mock catalogues that resemble the Kilo-Degree 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 cross-correlation 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 auto-correlation measurements and self-consistency relations, and will not become a dominant source of systematic error until the arrival of Stage-IV cosmic shear surveys. Using redshift distributions from a direct colour-based 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 real-world applications will require more sophisticated (parameterised) models of the redshift distribution in the future. If such better models are available, the clustering-redshift technique promises to be a highly complementary alternative to other methods of redshift calibration.

Authors 10

1. Jan Luca van den Busch

   University of Bonn · Ruhr University Bochum

   Affiliation as printed

   Argelander-Institut für Astronomie , Universität Bonn , Auf dem Hügel 71 , 53121 Bonn , Germany

   Ruhr-University Bochum , Astronomical Institute , German Centre for Cosmological Lensing , Universitätsstr. 150 , 44801 Bochum , Germany

   Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany

   Ruhr-University Bochum, Astronomical Institute, German Centre for Cosmological Lensing, Universitätsstr. 150, 44801 Bochum, Germany

2. Hendrik Hildebrandt

   Ruhr University Bochum

   Affiliation as printed

   Ruhr-University Bochum , Astronomical Institute , German Centre for Cosmological Lensing , Universitätsstr. 150 , 44801 Bochum , Germany

   Ruhr-University Bochum, Astronomical Institute, German Centre for Cosmological Lensing, Universitätsstr. 150, 44801 Bochum, Germany

3. Angus H. Wright

   Ruhr University Bochum

   Affiliation as printed

   Ruhr-University Bochum , Astronomical Institute , German Centre for Cosmological Lensing , Universitätsstr. 150 , 44801 Bochum , Germany

   Ruhr-University Bochum, Astronomical Institute, German Centre for Cosmological Lensing, Universitätsstr. 150, 44801 Bochum, Germany

4. Christopher Morrison

   University of Washington

   Affiliation as printed

   Department of Astronomy , University of Washington , Box 351580 , Seattle , WA 98195 , USA

   Department of Astronomy, University of Washington, Box 351580, Seattle, WA 98195, USA

5. Chris Blake

   Swinburne University of Technology

   Affiliation as printed

   Centre for Astrophysics & Supercomputing , Swinburne University of Technology , PO Box 218 , Hawthorn , VIC 3122 , Australia

   Centre for Astrophysics & Supercomputing, Swinburne University of Technology, PO Box 218, Hawthorn, VIC 3122, Australia

6. Benjamin Joachimi

   University College London

   Affiliation as printed

   Department of Physics and Astronomy , University College London , Gower Street , London WC1E 6BT , UK

   Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK

7. T. Erben

   University of Bonn

   Affiliation as printed

   Argelander-Institut für Astronomie , Universität Bonn , Auf dem Hügel 71 , 53121 Bonn , Germany

   Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany

8. Catherine Heymans

   Royal Observatory · Ruhr University Bochum · University of Edinburgh

   Affiliation as printed

   Institute for Astronomy , University of Edinburgh , Royal Observatory , Blackford Hill , Edinburgh EH9 3HJ , UK

   Ruhr-University Bochum , Astronomical Institute , German Centre for Cosmological Lensing , Universitätsstr. 150 , 44801 Bochum , Germany

   Institute for Astronomy, University of Edinburgh, Royal Observatory, Blackford Hill, Edinburgh EH9 3HJ, UK

   Ruhr-University Bochum, Astronomical Institute, German Centre for Cosmological Lensing, Universitätsstr. 150, 44801 Bochum, Germany

9. Konrad H. Kuijken Aachen Leiden Observatory

   Leiden University · Leiden Observatory

   Affiliation as printed

   Leiden Observatory , Leiden University , PO Box 9513 , 2300RA Leiden , The Netherlands

   Leiden Observatory, Leiden University, PO Box 9513, 2300RA Leiden, The Netherlands

10. Edward N. Taylor Aachen Leiden Observatory

    Leiden University · Leiden Observatory

    Affiliation as printed

    Leiden Observatory , Leiden University , PO Box 9513 , 2300RA Leiden , The Netherlands

    Leiden Observatory, Leiden University, PO Box 9513, 2300RA Leiden, The Netherlands