Optically-selected clusters at 0.8 1.3 in the EIS cluster survey

Free access article

Issue		A&A Volume 394, Number 1, October IV 2002


Page(s)		1 - 5
Section		Cosmology
DOI		http://dx.doi.org/10.1051/0004-6361:20021066

A&A 394, 1-5 (2002)
DOI: 10.1051/0004-6361:20021066

Optically-selected clusters at 0.8 $\la$ $\mathsfsl z$ $\la$ 1.3 in the EIS cluster survey

C. Benoist¹, L. da Costa², H. E. Jørgensen³, L. F. Olsen³, S. Bardelli⁴, E. Zucca⁴, M. Scodeggio⁵, D. Neumann⁶, M. Arnaud⁶, S. Arnouts², A. Biviano⁷ and M. Ramella⁷

¹ Observatoire de la Côte d'Azur, CERGA, BP 229, 06304 Nice Cedex 4, France
² European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching b. München, Germany
³ Astronomical Observatory, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
⁴ INAF - Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
⁵ Istituto di Fisica Cosmica - CNR, Milano, Italy
⁶ SAp, CEA/Saclay, L'Orme des Merisiers, Bât. 709, 91191 Gif-sur-Yvette Cedex, France
⁷ INAF - Osservatorio Astronomico di Trieste, Via G. B. Tiepolo 11, 34131 Trieste, Italy

(Received 7 December 2001 / Accepted 19 July 2002)

Abstract
This paper presents preliminary results of a spectroscopic survey being conducted at the VLT of fields with optically-selected cluster candidates identified in the EIS I-band survey. Here we report our findings for three candidates selected for having estimated redshifts in the range z= 0.8-1.1. New multi-band optical/infrared data were used to assign photometric redshifts to galaxies in the cluster fields and to select possible cluster members in preparation of the spectroscopic observations. Based on the available spectroscopic data, which includes 147 new redshifts for galaxies with $I_{AB}\la22$ -23, we confirm the detection of four density enhancements at a confidence level > $99\%$ . The detected concentrations include systems with redshifts z=0.81, z=0.95, z=1.14 and the discovery of the first optically-selected cluster at z=1.3. The latter system, with three concordant redshifts, coincides remarkably well with the location of a firm X-ray detection ( > $5\sigma$ ) in a ~80 ksec XMM-Newton image taken as part of this program which will be presented in a future paper (Neumann et al. in prep.). The z>1 systems presented here are possibly the most distant identified so far by their optical properties alone.

Key words: galaxies: clusters: individual: EIS0046-2930, EIS0533-2412, EIS0954-2023 -- large-scale structure of Universe -- cosmology: observations

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