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Published October 21, 2006 | Published
Journal Article Open

The Zurich Extragalactic Bayesian Redshift Analyzer and its first application: COSMOS


We present the Zurich Extragalactic Bayesian Redshift Analyzer (ZEBRA). The current version of ZEBRA combines and extends several of the classical approaches to produce accurate photometric redshifts down to faint magnitudes. In particular, ZEBRA uses the template-fitting approach to produce Maximum Likelihood and Bayesian redshift estimates based on the following points. (i) An automatic iterative technique to correct the original set of galaxy templates to best represent the Spectral Energy Distributions (SEDs) of real galaxies at different redshifts. (ii) A training set of spectroscopic redshifts for a small fraction of the photometric sample to improve the robustness of the photometric redshift estimates. (iii) An iterative technique for Bayesian redshift estimates, which extracts the full two-dimensional redshift and template probability function for each galaxy. We demonstrate the performance of ZEBRA by applying it to a sample of 866 I_AB ⩽ 22.5 COSMOS galaxies with available u*, B, V, g', r', i', z' and K_s photometry and zCOSMOS spectroscopic redshifts in the range 0 < z < 1.3 . Adopting a 5σ clipping that excludes ⩽10 galaxies, both the Maximum Likelihood and Bayesian ZEBRA estimates for this sample have an accuracy σ_(Δz/(1+z)) smaller than 0.03. Similar accuracies are recovered using mock galaxies.

Additional Information

© 2006 The Authors. Journal compilation © 2006 RAS. Accepted 2006 August 2. Received 2006 July 1; in original form 2006 May 8. We thank the anonymous referee for the helpful comments, which have improved the presentation of this paper, and Manfred Kitzbichler for making available to the COSMOS collaboration the mock catalogue used in this work. This work is based on observations taken with the following. (i) The NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by AURA, Inc., under NASA contract NAS 5-26555. (ii) The Subaru Telescope, which is operated by the National Astronomical Observatory of Japan. (iii) Facilities at the European Southern Observatory, Chile. (iv) Facilities at the Cerro Tololo Inter-American Observatory and at the National Optical Astronomy Observatory, which are operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation. (v) The CFHT operated by the National Research Council of Canada, the Centre National de la Recherche Scientifique de France and the University of Hawaii. T. Lisker is acknowledged for helping with a preliminary reduction of a fraction of the ground-based near-IR data.

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