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Astron. Astrophys. 343, L29-L34 (1999)


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Letter to the Editor

VLT and NTT observations of two EIS cluster candidates

Detection of the early-type galaxies sequence at [FORMULA] *

L. da Costa 1, M. Scodeggio 1, L.F. Olsen 1,2, M. Nonino 1,3, R. Rengelink 1, R. Bender 4, M. Franx 5, H.E. Jorgensen 2, A. Renzini 1 and P. Rosati 1

1 European Southern Observatory, Karl-Schwarzschild-Strasse 2, D-85748 Garching bei München, Germany
2 Astronomisk Observatorium, Juliane Maries Vej 30, DK-2100 Copenhagen, Denmark
3 Osservatorio Astronomico di Trieste, Via G.B. Tiepolo 11, I-31144 Trieste, Italy
4 Universitäts-Sternwarte München, Scheinerstrasse 1, D-81679 München, Germany
5 Leiden Observatory, P.O. Box 9513, 2300 RA, Leiden, The Netherlands

Received 1 December 1998 / Accepted 19 January 1999

Abstract

Optical data from the ESO VLT-UT1 Science Verification observations are combined with near-infrared data from SOFI at the NTT to obtain optical-infrared color-magnitude diagrams for the objects in the fields of two EIS cluster candidates. In both cases, evidence is found for a well-defined sequence of red galaxies that appear to be significantly more clustered than the background population. These results suggest that the two systems are real physical associations. The [FORMULA], [FORMULA] and [FORMULA] colors of the red sequences are used, in conjunction with similar data for spectroscopically confirmed clusters, to obtain redshift estimates of [FORMULA] and [FORMULA] for these two systems. These results make these EIS cluster candidates prime targets for follow-up spectroscopic observations to confirm their reality and to measure more accurately their redshift.

Key words: galaxies: clusters: general – cosmology: large-scale structure of Universe – cosmology: observations

* Based on observations collected at the European Southern Observatories of Paranal (VLT-UT1 Science Verification Program) and La Silla (Chile).

Send offprint requests to: L. da Costa

© European Southern Observatory (ESO) 1999

Online publication: March 1, 1999

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