First simultaneous optical/near-infrared imaging of an X-ray selected, high-redshift cluster of galaxies with GROND: The galaxy population of XMMU J0338.7 + 0030 at z = 1.1

Creators: Pierini, D.; Salvato, M.

Abstract

Context. The XMM-Newton Distant Cluster Project is a serendipitous survey for clusters of galaxies at redshifts z ≥ 0.8 based on deep archival XMM-Newton observations. X-ray sources identified as extended are screened against existing optical all-sky surveys for galaxies, in case of candidate high-z clusters followed up with imaging at 4 m-class telescopes and, ultimately, multi-object spectroscopy at 8 m-class telescopes. Low-significance candidate high-z clusters are followed up with the seven-channel imager GROND (Gamma-Ray Burst Optical and Near-Infrared Detector) that is mounted at a 2 m-class telescope. Its unique capability of simultaneous imaging in the g′,r′,i′,z′,J,H,Ks bands enables the use of the photometric redshift technique. Aims. Observing strategy, data reduction and analysis, depth and accuracy of the simultaneous multi-wavelength photometry are discussed with the goal of establishing GROND as a useful instrument to confirm X-ray selected (high-z) clusters. Methods. The test case is XMMU J0338.7 + 0030, suggested to be at z ~ 1.45 ± 0.15 (1σ) from the analysis of the z − H vs. H colour − magnitude diagram obtained from the follow-up imaging. Later VLT-FORS2 spectroscopy enabled us to identify four members, which set this cluster at z = 1.097 ± 0.002 (1σ). To reach a better knowledge of its galaxy population, we observed XMMU J0338.7 + 0030 with GROND for about 6 h. The publicly available photo-z code le Phare was used. Results. The Ks-band number counts of the non-stellar sources out of the 832 detected down to z′ ~ 26 AB mag (1σ) in the 3.9 × 4.3 arcmin^2 region of XMMU J0338.7 + 0030 imaged at all GROND bands clearly exceed those computed in deep fields/survey areas at ~20.5–22.5 AB mag. The photo-z's of the three imaged spectroscopic members yield z = 1.12 ± 0.09 (1σ). The spatial distribution and the properties of the GROND sources with a photo-z in the range 1.01–1.23 confirm the correspondence of the X-ray source with a galaxy over-density at a significance of at least 4.3σ. Candidate members that are spectro-photometrically classified as elliptical galaxies define a red locus in the i′ − z′ vs. z′ colour − magnitude diagram that is consistent with the red sequence of the cluster RDCS J0910 + 5422 at z = 1.106. XMMU J0338.7 + 0030 hosts also a population of bluer late-type spirals and irregulars. The starbursts among the photometric members populate both loci, consistently with previous results. Conclusions. The analysis of the available data set indicates that XMMU J0338.7 + 0030 is a low-mass cluster (M_200 ~ 10^(14) M_⊙) at z = 1.1. With the photometric accuracy yielded by the present unoptimized multi-band observations with GROND, we not only confirm the spectroscopic redshift of this cluster but also show that it hosts a galaxy population that can still undergo significant bursts of star-formation activity.

Additional Information

© 2012 ESO. Article published by EDP Sciences. Received 8 February 2011; Accepted 13 December 2011. Published online 23 March 2012. D.P. thanks the anonymous referee for her/his insightful comments, which led to a signficant improvement on the robustness and presentation quality of the results in the final version of the paper. This research was supported by the DFG cluster of excellence "Origin and Structure of the Universe" (http://www.universe-cluster.de) through EXC project number 153, the DFG under grants Schw 536/24-1, Schw 536/24-2, BO 702/16-3, and the DLR under grants 50 OR 0405 and 50 QR 0802. R.S. acknowledges support by the DFG in the program SPP 1177. H.Q. thanks the FONDAP Centro de Astrofísica for partial support. F.Z. acknowledges support from and participation in the International Max-Plank Research School on Astrophysics at the Ludwig-Maximilians University. D.P. acknowledges useful feedback from O. Ilbert. D.P. acknowledges the kind hospitality at the Max-Planck-Institut für extraterrestrische Physik (MPE). This research has made use of observations collected at the European Organisation for Astronomical Research in the Southern Hemisphere (ESO), Chile (079.A−0634). This research has made use of observations collected at the Centro Astronómico Hispano Alemán (CAHA) at Calar Alto, Spain operated jointly by the Max-Planck-Institut für Astronomie and the Istituto de Astrofísica de Andalucía (CSIC). This work has made use of the SDSS database. Funding for the SDSS and SDSS-II has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation, the US Department of Energy, the National Aeronautics and Space Administration, the Japanese Monbukagakusho, the Max Planck Society, and the Higher Education Funding Council for England. The SDSSWeb Site is http://www.sdss.org/. The SDSS is managed by the Astrophysical Research Consortium for the Participating Institutions. The Participating Institutions are the American Museum of Natural History, Astrophysical Institute Potsdam, University of Basel, University of Cambridge, Case Western Reserve University, University of Chicago, Drexel University, Fermilab, the Institute for Advanced Study, the Japan Participation Group, Johns Hopkins University, the Joint Institute for Nuclear Astrophysics, the Kavli Institute for Particle Astrophysics and Cosmology, the Korean Scientist Group, the Chinese Academy of Sciences (LAMOST), Los Alamos National Laboratory, the Max-Planck- Institute for Astronomy (MPIA), the Max-Planck-Institute for Astrophysics (MPA), New Mexico State University, Ohio State University, University of Pittsburgh, University of Portsmouth, Princeton University, the United States Naval Observatory, and the University of Washington. This publication makes use of data products from the TwoMicron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. This research has made use of the NASA/IPAC Extragalactic Data base (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.

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