Galaxy clusters in the CFHTLS^*

II. Matched-filter results in different passbands

¹ Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark e-mail: lisbeth@dark-cosmology.dk
² Observatoire de la Côte d'Azur, Laboratoire Cassiopée, BP 4229, 06304 Nice Cedex 4, France

Received: 13 June 2008
Accepted: 7 November 2008

Abstract

Aims. We investigate the gain of added leverage and completeness of the constructed cluster catalogue, of applying the matched-filter detection algorithm to multiple passbands. In particular, we investigate the gain from having both i'- and z'-band data available when searching for galaxy clusters at .

Methods. We applied a matched filter detection method to the CFHTLS r'- and z'-band data of the four Deep fields and compared the cluster catalogues with the one extracted from the i'-band data presented in a previous paper. We also applied the matched filter to the Deep fields but with the limiting magnitudes appropriate for the much larger Wide survey in order to understand the best combination of i'- and z'-band depth for the most efficient cluster searches based on this algorithm.

Results. The density of clusters identified in the Deep r'- and z'-band catalogues are 36 and 80 per square degree, respectively. The estimated densities of false detections are 12 and 20 per square degree in the two bands. We find that the recovered properties are in good agreement between the different bands and also that the efficiency of each band is consistent with the expectations based on the shift of the 4000 Å break through the filters. When comparing r'- and i'-band, we do not find any significant additions to the i'-band catalogue. On the contrary, we find a large number of high redshift detections in the z'-band not in i'. These detections add to the number of high-redshift detections in the i'-band.

Conclusions. We conclude that, for cluster searches to redshifts 1, it is important to include sufficiently deep data redward of the i'-band, which in this work is provided by the z'-band coverage. The combination of catalogues extracted from two different passbands does not provide a cluster sample with greater purity.