Structure and substructure analysis of DAFT/FADA galaxy clusters in the [0.4–0.9] redshift range^⋆

¹ Aix-Marseille Université, CNRS, LAM (Laboratoire d’Astrophysique de Marseille) UMR 7326, 13388 Marseille, France
e-mail: guennou@ukzn.ac.za
² Astrophysics and Cosmology Research Unit, University of KwaZulu-Natal, 4041 Durban, South Africa
³ UPMC-CNRS, UMR7095, Institut d’Astrophysique de Paris, 75014 Paris, France
⁴ Departamento de Astronomia, Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, Rua do Matão 1226, 05508-900 São Paulo, Brazil
⁵ Dept of Physics and Astronomy & Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA), Evanston IL 60208-2900, USA
⁶ Department of Physics and Astronomy, Ohio University, 251B Clippinger Lab, Athens OH 45701, USA
⁷ Fermi National Accelerator Laboratory, PO Box 500, Batavia IL 60510, USA
⁸ CSC/STScI, 3700 San Martin Dr., Baltimore MD 21218, USA
⁹ OCA, Cassiopée, Boulevard de l’Observatoire, BP 4229, 06304 Nice Cedex 4, France
¹⁰ INAF/Osservatorio Astronomico di Trieste, via Tiepolo 11, 34143 Trieste, Italy
¹¹ INAF – Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
¹² 23 rue d’Yerres, 91230 Montgeron, France
¹³ Steward Observatory, University of Arizona, 933 N. Cherry Ave., Tucson AZ 85721, USA
¹⁴ Department of Astronomy & Astrophysics, University of Toronto, 50 St George Street, Toronto M5S 3H4, Canada
¹⁵ Instituto de Astrofísica de Andalucía, CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
¹⁶ Laboratório de Astrofísica Teórica e Observacional, Universidade Estadual de Santa Cruz, 45662-000 Ilhéus, Brazil
¹⁷ Gemini Observatory, 603 Casilla, La Serena, Chile
¹⁸ Argelander-Institut für Astronomie, Universität Bonn, auf dem Hügel 71, 53121 Bonn, Germany
¹⁹ University of Vienna, Department of Astronomy, Türkenschanzstrasse 17, 1180 Vienna, Austria

Received: 31 January 2013
Accepted: 25 October 2013

Abstract

Context. The DAFT/FADA survey is based on the study of ~90 rich (masses found in the literature >2 × 10¹⁴   M_⊙) and moderately distant clusters (redshifts 0.4 < z < 0.9), all with HST imaging data available. This survey has two main objectives: to constrain dark energy (DE) using weak lensing tomography on galaxy clusters and to build a database (deep multi-band imaging allowing photometric redshift estimates, spectroscopic data, X-ray data) of rich distant clusters to study their properties.

Aims. We analyse the structures of all the clusters in the DAFT/FADA survey for which XMM-Newton and/or a sufficient number of galaxy redshifts in the cluster range are available, with the aim of detecting substructures and evidence for merging events. These properties are discussed in the framework of standard cold dark matter (ΛCDM) cosmology.

Methods. In X-rays, we analysed the XMM-Newton data available, fit a β-model, and subtracted it to identify residuals. We used Chandra data, when available, to identify point sources. In the optical, we applied a Serna & Gerbal (SG) analysis to clusters with at least 15 spectroscopic galaxy redshifts available in the cluster range. We discuss the substructure detection efficiencies of both methods.

Results. XMM-Newton data were available for 32 clusters, for which we derive the X-ray luminosity and a global X-ray temperature for 25 of them. For 23 clusters we were able to fit the X-ray emissivity with a β-model and subtract it to detect substructures in the X-ray gas. A dynamical analysis based on the SG method was applied to the clusters having at least 15 spectroscopic galaxy redshifts in the cluster range: 18 X-ray clusters and 11 clusters with no X-ray data. The choice of a minimum number of 15 redshifts implies that only major substructures will be detected. Ten substructures were detected both in X-rays and by the SG method. Most of the substructures detected both in X-rays and with the SG method are probably at their first cluster pericentre approach and are relatively recent infalls. We also find hints of a decreasing X-ray gas density profile core radius with redshift.

Conclusions. The percentage of mass included in substructures was found to be roughly constant with redshift values of 5–15%, in agreement both with the general CDM framework and with the results of numerical simulations. Galaxies in substructures show the same general behaviour as regular cluster galaxies; however, in substructures, there is a deficiency of both late type and old stellar population galaxies. Late type galaxies with recent bursts of star formation seem to be missing in the substructures close to the bottom of the host cluster potential well. However, our sample would need to be increased to allow a more robust analysis.