A&A 380, 460-470 (2001)
DOI: 10.1051/0004-6361:20011457
On the nature of the EIS candidate clusters: Confirmation of
0.6 candidates
L. F. Olsen1, C. Benoist2, L. da Costa3, M. Scodeggio4, H. E. Jørgensen1, S. Arnouts3, S. Bardelli5, A. Biviano6, M. Ramella6 and E. Zucca5
1 Astronomical Observatory, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark
2 Observatoire de la Côte d'Azur, BP 229, 06304 Nice Cedex 4, France
3 European Southern Observatory, Karl-Schwartzschild-Strasse 2, 85748 Garching bei München, Germany
4 Istituto di Fisica Cosmica, via Bassini 15, 20133 Milano, Italy
5 Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
6 INAF, Osservatorio Astronomico di Trieste, via G.B. Tiepolo, 11, 34131 Trieste, Italy
(Received 3 September 2001 / Accepted 15 October 2001)
Abstract
We use publicly available V-band imaging data from the
wide-angle surveys conducted by the ESO Imaging Survey project (EIS)
to further investigate the nature of the EIS galaxy cluster
candidates. These were originally identified by applying a
matched-filter algorithm which used positional and photometric data of
the galaxy sample extracted from the I-band survey images. In this
paper, we apply the same technique to the galaxy sample extracted from
V-band data and compare the new cluster detections with the original
ones. We find that ~75% of the low-redshift cluster candidates
(
) are detected in both passbands and their estimated
redshifts show good agreement with the scatter in the redshift
differences being consistent with the estimated errors of the
method. For the "robust" I-band detections the matching frequency
approaches ~85% . We also use the available (V-I) color to
search for the red sequence of early-type galaxies observed in rich
clusters over a broad range of redshifts. This is done by searching
for a simultaneous overdensity in the three-dimensional
color-projected distance space. We find significant overdensities for
~75% of the "robust" candidates with
. We find
good agreement between the characteristic color associated to the
detected "red sequence" and that predicted by passive evolution galaxy
models for ellipticals at the redshift estimated by the
matched-filter. The results presented in this paper show the
usefulness of color data, even of two-band data, to both tentatively
confirm cluster candidates and to select possible cluster members for
spectroscopic observations. Based on the present results, we estimate
that ~150 EIS clusters with
are real, making it
one of the largest samples of galaxy clusters in this redshift range
currently available in the southern hemisphere.
Key words: galaxies: clusters: general -- large-scale structure of Universe -- cosmology: observations
Offprint request: L. F. Olsen, lisbeth@astro.ku.dk
© ESO 2001