CLASH: Photometric redshifts with 16 HST bands in galaxy cluster fields ^⋆,⋆⋆

¹ Institut de Ciències de l’Espai (IEEC-CSIC), 08193 Bellaterra ( Barcelona), Spain
e-mail: jouvel@ice.cat
² University College London, Gower street, London WC1E 6BT, UK
³ Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
⁴ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore MD 21218, USA
⁵ European Southern Observatory (ESO), 85748 Garching, Germany
⁶ Institut für Astronomie und Astrophysik, Universitäts-Sternwarte München, 81679 München, Germany
⁷ Department of Theoretical Physics, University of the Basque Country UPV/EHU, 48080 Bilbao, Spain
⁸ Ikerbasque, Basque Foundation for Science, 48011 Bilbao, Spain
⁹ Instituto de Astrofísica de Andalucía (IAA-CSIC), 18008 Granada, Spain
¹⁰ Department of Physics and Astronomy, The Johns Hopkins University, Baltimore, MD, USA
¹¹ Institut für Theoretische Astrophysik, Zentrum für Astronomie, Institut für Theoretische Astrophysik, Albert-Ueberle-Str. 2, 29120 Heidelberg, Germany
¹² Leiden Observatory, Leiden University, 2333 Leiden, The Netherlands
¹³ Department of Physics and Astronomy, Michigan State University, East Lansing, MI, USA
¹⁴ Department of Astronomy, University of California, Berkeley CA 94720, USA
¹⁵ Instituto de Astrofísica y AIUC, P. Universidad Católica de Chile, 306 Casilla, Santiago 22, Chile
¹⁶ Carnegie Observatories, Carnegie Institute for Science, Pasadena, CA, USA
¹⁷ Center for Cosmology and Astro-Particle Physics, The Ohio State University, 191 W. Woodruff Ave., Columbus OH 43210, USA
¹⁸ INAF – Osservatorio Astronomico di Bologna, INFN, Sezione di Bologna, 40127 Bologna, Italy
¹⁹ Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr, Pasadena, CA 91109, USA
²⁰ Institute of Astronomy and Astrophysics, Academia Sinica, PO Box 23-141, 10617 Taipei, Taiwan
²¹ INAF – Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy
²² Department of Physics and Astronomy, Siena College, 515 Loudon Road, Loudonville NY 12211, USA
²³ INAF – Istituto di Astrofisica Spaziale e Fisica cosmica (IASF) Milano, via Bassini 15, 20133 Milano, Italy
²⁴ Cahill Center for Astronomy and Astrophysics, California Institute of Technology, MS 249-17, Pasadena CA 91125, USA
²⁵ INAF – Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, 40131 Trieste, Italy
²⁶ Hubble Fellow 

Received: 31 July 2013
Accepted: 22 November 2013

Abstract

Context. The Cluster Lensing And Supernovae survey with Hubble (CLASH) is a Hubble Space Telescope (HST) Multi-Cycle Treasury programme thatobserves 25 massive galaxy clusters, 20 of which were X-ray-selected to preferably choose dynamically relaxed clusters, and 5 additional “high magnification” clusters, which were selected based on their optical lensing properties. CLASH aims to study the dark matter distribution of the clusters and find magnified high-redshift galaxies behind them. CLASH observations were carried out in 16 bands from UV to NIR to derive accurate and reliable estimates of photometric redshifts.

Aims. We present the CLASH photometric redshifts using 16 HST bands and study the photometric redshift accuracy including a detailed comparison between photometric and spectroscopic redshifts for the strong lensing arcs using the measurements from the cluster MACSJ1206.2-0847.

Methods. We used the publicly available Le Phare and BPZ photometric redshift estimation codes on 17 CLASH galaxy clusters for which the full photo-z data processing had been completed at the time of this analysis, and derive an estimate of the CLASH photo-z accuracy.

Results. Using Le Phare code for objects with a S/N ≥ 10, we reach a precision of 3%(1 + z) for the strong lensing arcs, which is reduced to 2.4%(1 + z) after removing outliers. For galaxies in the cluster field, the corresponding values are 4%(1 + z) and 3%(1 + z). Using mock galaxy catalogues, we show that 3%(1 + z) precision is what is expected using the baseline sky substraction algorithm when taking into account extinction from dust, emission lines, and the finite range of SEDs included in the photo-z template library. An improved method for estimating galaxy colours that yields more accurate photometric redshifts will be explored in a forthcoming paper. We study photo-z results for different aperture photometry techniques and find that the SExtractor isophotal photometry works best. We check the robustness of the arcs photo-z results by rederiving the input photometry in the case of MACS1206. We describe and release a photometric redshift catalogue of the MACS1206 cluster we study.

Conclusions. Our photo-z codes give similar results for the strong lensing arcs, as well as for galaxies of the cluster field. Results are improved when optimizing the photometric aperture shape that shows an optimal aperture size around 1′′ radius, giving results that are equivalent to isophotal photometry. Tailored photometry of the arcs improves the photo-z results by showing more consistency between the different arcs of the same strong lensing system.