The DAFT/FADA survey

I. Photometric redshifts along lines of sight to clusters in the z = [0.4, 0.9] interval^⋆

¹ LAM, OAMP, Pôle de l’Etoile Site de Château-Gombert, 38 rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France
e-mail: christophe.adami@oamp.fr
² Department Physics Astronomy, Northwestern University, Evanston, IL 60208-2900, USA
³ UPMC Université Paris 06, UMR 7095, Institut d’Astrophysique de Paris, 75014 Paris, France
⁴ CNRS, UMR 7095, Institut d’Astrophysique de Paris, 75014 Paris, France
⁵ Department of Physics and Astronomy, Ohio University, 251B Clippinger Lab, Athens, OH 45701, USA
⁶ Fermi National Accelerator Laboratory, PO Box 500, Batavia, IL 60510, USA
⁷ OCA, Cassiopée, Boulevard de l’Observatoire, BP 4229, 06304 Nice Cedex 4, France
⁸ INAF/Osservatorio Astronomico di Trieste, via G. B. Tiepolo 11, 34143 Trieste, Italy
⁹ INAF - Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
¹⁰ Leiden Observatory, Leiden University, Niels Bohrweg 2, 2333 CA Leiden, The Netherlands
¹¹ Kavli Institute for Particle Astrophysics and Cosmology, Stanford University, 2575 Sand Hill Road, Menlo Park, CA 94025, USA
¹² Physics Department, University of California, Santa Barbara, CA 93601, USA

Received: 8 June 2010
Accepted: 9 August 2010

Abstract

Context. As a contribution to the understanding of the dark energy concept, the Dark energy American French Team (DAFT, in French FADA) has started a large project to characterize statistically high redshift galaxy clusters, infer cosmological constraints from weak lensing tomography, and understand biases relevant for constraining dark energy and cluster physics in future cluster and cosmological experiments.

Aims. The purpose of this paper is to establish the basis of reference for the photo-z determination used in all our subsequent papers, including weak lensing tomography studies.

Methods. This project is based on a sample of 91 high redshift (z ≥ 0.4), massive (≳3 × 10¹⁴   M_⊙) clusters with existing HST imaging, for which we are presently performing complementary multi-wavelength imaging. This allows us in particular to estimate spectral types and determine accurate photometric redshifts for galaxies along the lines of sight to the first ten clusters for which all the required data are available down to a limit of I_AB = 24./24.5 with the LePhare software. The accuracy in redshift is of the order of 0.05 for the range 0.2 ≤ z ≤ 1.5.

Results. We verified that the technique applied to obtain photometric redshifts works well by comparing our results to with previous works. In clusters, photo-z accuracy is degraded for bright absolute magnitudes and for the latest and earliest type galaxies. The photo-z accuracy also only slightly varies as a function of the spectral type for field galaxies. As a consequence, we find evidence for an environmental dependence of the photo-z accuracy, interpreted as the standard used spectral energy distributions being not very well suited to cluster galaxies. Finally, we modeled the LCDCS 0504 mass with the strong arcs detected along this line of sight.