Distant galaxy clusters in a deep XMM-Newton field within the CFTHLS D4 ^{⋆,⋆⋆,⋆⋆⋆}

¹ Leibniz-Institut für Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
e-mail: arjen@aip.de
² Max-Planck-Institut für extraterrestische Physik, Giessenbachstraße, 85748 Garching, Germany
³ European Space Astronomy Center (ESAC)/ESA, Madrid, Spain
⁴ Departamento de Astronomá y Astrofísica, Pontificia Universidad Católica de Chile, Casilla 306, 22 Santiago, Chile
⁵ National Research Institute of Astronomy and Geophysics (NRIAG), Helwan, Cairo, Egypt
⁶ University Observatory Munich, Ludwig-Maximillians University Munich, Scheinerstr. 1, 81679 Munich, Germany
⁷ Institut für Astronomie, Universität Wien, Universitätsring 1, 1010 Wien, Austria

Received: 15 September 2012
Accepted: 6 December 2012

Abstract

Aims. The XMM-Newton distant cluster project (XDCP) aims at the identification of a well defined sample of X-ray selected clusters of galaxies at redshifts z ≥ 0.8. As part of this project, we analyse the deep XMM-Newton exposure covering one of the CFHTLS deep fields to quantify the cluster content. We validate the optical follow-up strategy as well as the X-ray selection function.

Methods. We searched for extended X-ray sources in archival XMM-Newton EPIC observations. Multi-band optical imaging was performed to select high redshift cluster candidates among the extended X-ray sources. Here we present a catalogue of the extended sources in one the deepest  ~250 ks XMM-Newton fields targetting LBQS 2212-1759 covering  ~0.2deg². The cluster identification is based on deep imaging with the ESO VLT and from the CFHT legacy survey, among others. The confirmation of cluster candidates is done by VLT/FORS2 multi-object spectroscopy. Photometric redshifts from the CFHTLS D4 were utilised to confirm the effectiveness of the X-ray cluster selection method. The survey sensitivity was computed with extensive Monte-Carlo simulations.

Results. At a flux limit of S_{0.5 − 2.0   keV} ~ 2.5 × 10^-15ergs^-1 we achieve a completeness level higher than 50% in an area of  ~ 0.13   deg². We detect six galaxy clusters above this limit with optical counterparts, of which 5 are new spectroscopic discoveries. Two newly discovered X-ray luminous galaxy clusters are at z ≥ 1.0, another two at z = 0.41, and one at z = 0.34. For the most distant X-ray selected cluster in this field at z = 1.45, we find additional (active) member galaxies from both X-ray and spectroscopic data. Additionally, we find evidence of large-scale structures at moderate redshifts of z = 0.41 and z = 0.34.

Conclusions. The quest for distant clusters in archival XMM-Newton data has led to detection of six clusters in a single field, making XMM-Newton an outstanding tool for cluster surveys. Three of these clusters are at z ≥ 1, which emphasises the valuable contribution of small, yet deep surveys to cosmology. Beta models are appropriate descriptions of the cluster surface brightness when performing cluster detection simulations to compute the X-ray selection function. The constructed log N − log S tends to favour a scenario where no evolution in the cluster X-ray luminosity function (XLF) takes place.