MAPPING THE GALAXY COLOR–REDSHIFT RELATION: OPTIMAL PHOTOMETRIC REDSHIFT CALIBRATION STRATEGIES FOR COSMOLOGY SURVEYS
- Infrared Processing and Analysis Center, California Institute of Technology, Pasadena, CA 91125 (United States)
- Spitzer Science Center, California Institute of Technology, Pasadena, CA 91125 (United States)
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109 (United States)
- Aix Marseille Universite, CNRS, LAM (Laboratoire dAstrophysique de Marseille) UMR 7326, F-13388, Marseille (France)
- Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse, D-85748 Garching (Germany)
- Department of Physics, University of California, Davis, CA 95616 (United States)
- Department of Physics, University Federico II, via Cinthia 6, I-80126 Napoli (Italy)
- Department of Astronomy, University of Geneva ch. dcogia 16, CH-1290 Versoix (Switzerland)
- Department of Physics and Astronomy, University of California, Riverside, CA 92521 (United States)
- Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA, Leiden (Netherlands)
- Argelander-Institut für Astronomie, Universität Bonn, Auf dem H’´ugel 71, D-53121 Bonn (Germany)
- Department of Astronomy, Harvard University, 60 Garden Street, MS 46, Cambridge, MA 02138 (United States)
- Massachusetts Institute of Technology, Cambridge, MA 02139 (United States)
- Department of Physics and Astronomy, University of Missouri, Kansas City, MO 64110 (United States)
- Astronomical Observatory of Capodimonte—INAF, via Moiariello 16, I-80131, Napoli (Italy)
Calibrating the photometric redshifts of ≳10{sup 9} galaxies for upcoming weak lensing cosmology experiments is a major challenge for the astrophysics community. The path to obtaining the required spectroscopic redshifts for training and calibration is daunting, given the anticipated depths of the surveys and the difficulty in obtaining secure redshifts for some faint galaxy populations. Here we present an analysis of the problem based on the self-organizing map, a method of mapping the distribution of data in a high-dimensional space and projecting it onto a lower-dimensional representation. We apply this method to existing photometric data from the COSMOS survey selected to approximate the anticipated Euclid weak lensing sample, enabling us to robustly map the empirical distribution of galaxies in the multidimensional color space defined by the expected Euclid filters. Mapping this multicolor distribution lets us determine where—in galaxy color space—redshifts from current spectroscopic surveys exist and where they are systematically missing. Crucially, the method lets us determine whether a spectroscopic training sample is representative of the full photometric space occupied by the galaxies in a survey. We explore optimal sampling techniques and estimate the additional spectroscopy needed to map out the color–redshift relation, finding that sampling the galaxy distribution in color space in a systematic way can efficiently meet the calibration requirements. While the analysis presented here focuses on the Euclid survey, similar analysis can be applied to other surveys facing the same calibration challenge, such as DES, LSST, and WFIRST.
- OSTI ID:
- 22518729
- Journal Information:
- Astrophysical Journal, Vol. 813, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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