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

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 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 –23, we confirm the detection of four density enhancements at a confidence level > . The detected concentrations include systems with redshifts , , and the discovery of the first optically-selected cluster at . The latter system, with three concordant redshifts, coincides remarkably well with the location of a firm X-ray detection (> ) 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 systems presented here are possibly the most distant identified so far by their optical properties alone.