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Astron. Astrophys. 360, 896-910 (2000)

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EISily looking for distant clusters of galaxies - a new algorithm and its application to the EIS-wide data

C. Lobo 1,2, A. Iovino 1, D. Lazzati 1 and G. Chincarini 1

1 Osservatorio Astronomico di Brera, Via Brera 28, 20121 Milano, Italy
2 Observatório Astronómico de Lisboa, Tapada da Ajuda, 1349-018 Lisboa, Portugal

Received 27 April 2000 / Accepted 16 June 2000


We present a new algorithm to search for distant clusters of galaxies on catalogues deriving from imaging data, as those of the ESO Imaging Survey.

Our algorithm is a matched filter one, similar to that adopted by Postman et al. (1996), aiming at identifying cluster candidates by using positional and photometric data simultaneously. The main novelty of our approach is that spatial and luminosity filter are run separately on the catalogue and no assumption is made on the typical size nor on the typical [FORMULA] for clusters, as these parameters intervene in our algorithm as typical angular scale [FORMULA] and typical apparent magnitude [FORMULA]. Moreover we estimate the background locally for each candidate, allowing us to overcome the hazards of inhomogeneous datasets. As a consequence our algorithm has a lower contamination rate - without loss of completeness - in comparison to other techniques, as tested through extensive simulations. We provide catalogues of galaxy cluster candidates as the result of applying our algorithm to the I-band data of the EIS-wide patches A and B.

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

Send offprint requests to: C. Lobo (lobo@oal.ul.pt)

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© European Southern Observatory (ESO) 2000

Online publication: August 23, 2000