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Issue A&A Volume 442, Number 3, November II 2005 Page(s) 841 - 849 Section Cosmology (including clusters of galaxies) DOI 10.1051/0004-6361:20053433

A&A 442, 841-849 (2005)
DOI: 10.1051/0004-6361:20053433

New spectroscopic confirmations of high-redshift galaxy clusters

L. F. Olsen^{1, 2}, E. Zucca³, S. Bardelli³, C. Benoist¹, L. da Costa^{4, 5}, H. E. Jørgensen², A. Biviano⁶ and M. Ramella<sup>6

1</sup>  Observatoire de la Côte d'Azur, Laboratoire Cassiopée, BP 4229, 06304 Nice Cedex 4, France
²  Niels Bohr Institute, Copenhagen University, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
    e-mail: lisbeth@astro.ku.dk
³  INAF - Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
⁴  Observatorio Nacional, Rua General Jose Cristinino 77, CEP 20921-400, Rio de Janeiro JR, Brazil
⁵  European Southern Observatory, Karl-Schwartzschild-Str. 2, 85748 Garching b. München, Germany
⁶  INAF - Osservatorio Astronomico di Trieste, Via G.B. Tiepolo 11, 34131 Trieste, Italy

(Received 13 May 2005 / Accepted 21 July 2005 )

Abstract
We present new spectroscopic data in the field of five high-redshift () candidate galaxy clusters, drawn from the EIS Cluster Candidate Catalog. A total of 327 spectra were obtained using FORS1 at the VLT, out of which 266 are galaxies with secure redshifts. In this paper, we use these data for confirming the existence of overdensities in redshift space at the approximate same location as the matched-filter detections in the projected distribution of galaxies from the EIS I-band imaging survey. The spectroscopic redshifts, associated to these overdensities, are consistent but, in general, somewhat lower than those predicted by the matched-filter technique. Combining the systems presented here with those analyzed earlier, we have spectroscopically confirmed a total of nine overdensities in the redshift range 0.6 < z < 1.3, providing an important first step in building an optically-selected, high-redshift sample for more detailed studies, complementing those based on the few available X-ray selected systems.

Key words: cosmology: observations -- galaxies: distances and redshifts -- galaxies: clusters: general

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