Astronomy & Astrophysics

Free access article

Issue		A&A Volume 444, Number 3, December IV 2005
Page(s)		685 - 695
Section		Cosmology (including clusters of galaxies)
DOI		10.1051/0004-6361:20053449

A&A 444, 685-695 (2005)
DOI: 10.1051/0004-6361:20053449

VGCF detection of galaxy systems at intermediate redshifts

R. Barrena¹, M. Ramella², W. Boschin^{3, 4}, M. Nonino², A. Biviano² and E. Mediavilla¹

¹ Instituto de Astrofísica de Canarias, Vía Láctea s/n, 38200 La Laguna, Tenerife, Spain
e-mail: rbarrena@iac.es
² INAF, Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, 34131 Trieste, Italy
³ INAF, Telescopio Nazionale Galileo, Roque de Los Muchachos, PO box 565, 38700 Santa Cruz de La Palma, Spain
⁴ Dipartimento di Astronomia of the Università degli Studi di Trieste, via G.B. Tiepolo 11, 34131 Trieste, Italy

(Received 17 May 2005 / Accepted 10 August 2005 )

Abstract
We continue the development of our Voronoi Galaxy Cluster Finder (VGCF) technique by applying it to galaxy catalogs obtained with B and R band observations of four high galactic latitude fields of $0.5 \times 0.5$ square degrees each. These fields are deep ( $R_{{\rm lim}} \sim 23$ , $B_{{\rm lim}} \sim 26$ ) and partially overlap the Palomar Distant Cluster ${\it Survey}$ (PDCS) fields at 0 $^{{\rm h}}$ and 2 $^{{\rm h}}$ . We run the VGCF also on the original V and I band PDCS galaxy catalogs. We identify a total of 48 clusters that are particularly reliable, being detected in at least two bands. The analysis of color-magnitude diagrams and, in a few cases, spectroscopic observations allow us to further increase the reliability of 25 of the 48 clusters. For these 26 clusters we also estimate redshifts that fall in the approximate range 0.2 < z < 0.6. We detect 41 VGCF clusters within the strict limits of the PDCS fields at 0 $^{{\rm h}}$ and 2 $^{{\rm h}}$ . The PDCS catalog for the same regions consists of 28 clusters. The two catalogs have 20 clusters in common. These clusters together with the remaining PDCS and VGCF clusters lead to a total number of 46 "independent" clusters. The total number of clusters is therefore 20% larger than the number of VGCF clusters and more than 60% larger than the number of PDCS clusters. These results confirm a) that the VGCF is a competitive algorithm for the identification of optical clusters, and b) that a combined catalog of matched-filter and VGCF clusters constitutes a significant progress toward a more complete selection of clusters from bidimensional optical data.

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

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