Galaxy cluster searches based on photometric redshifts in the four CFHTLS Wide fields^⋆,⋆⋆

¹ UPMC Université Paris 06, UMR 7095, Institut d’Astrophysique de Paris, 98bis Bd Arago, 75014 Paris, France
e-mail: durret@iap.fr
² CNRS, UMR 7095, Institut d’Astrophysique de Paris, 75014 Paris, France
³ LAM, OAMP, Pôle de l’Étoile Site Château-Gombert, 38 rue Frédéric Juliot-Curie, 13388 Marseille Cedex 13, France
⁴ INAF – Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
⁵ OCA, Cassiopée, Boulevard de l’Observatoire, BP 4229, 06304 Nice Cedex 4, France
⁶ Instituto de Astrofísica de Andalucía (CSIC), Apdo. 3004, 18080 Granada, Spain
⁷ Astronomical Institute, Graduate School of Science, Tohoku University Sendai 980-8578, Japan
⁸ Canada-France-Hawaii Telescope Corporation, Kamuela, HI 96743, USA
⁹ CRAL (UMR 5574), Université Claude Bernard Lyon 1 (UCBL), École Normale Supérieure de Lyon (ENS-L), and Centre National de la Recherche Scientifique (CNRS), 69230 Saint-Genis Laval, France
¹⁰ Université Paris 07 Denis Diderot, 75205 Paris Cedex, France
¹¹ INAF IASF – Milano, via Bassini 15, 20133 Milano, Italy
¹² ENS-Cachan, 61 avenue du président Wilson, 94235 Cachan Cedex, France
¹³ Department of Physics & Astronomy, Northwestern University, Evanston, IL 60208-2900, USA

Received: 30 March 2011
Accepted: 1 September 2011

Abstract

Context. Cosmological parameters can be constrained by counting clusters of galaxies as a function of mass and redshift and by considering regions of the sky sampled as deeply and as homogeneously as possible.

Aims. Several methods for detecting clusters in large imaging surveys have been developed, among which the one used here, which is based on detecting structures. This method was first applied to the Canada France Hawaii Telescope Legacy Survey (CFHTLS) Deep 1 field by Mazure et al. (2007, A&A, 467, 49), then to all the Deep and Wide CFHTLS fields available in the T0004 data release by Adami et al. (2010, A&A, 509, A81). The validity of the cluster detection rate was estimated by applying the same procedure to galaxies from the Millennium simulation. Here we use the same method to analyse the full CFHTLS Wide survey, based on the T0006 data release.

Methods. Our method is based on the photometric redshifts computed with Le Phare for all the galaxies detected in the Wide fields, limited to magnitudes z′ ≤ 22.5. We constructed galaxy density maps in photometric redshift bins of 0.1 based on an adaptive kernel technique, detected structures with SExtractor at various detection levels, and built cluster catalogues by applying a minimal spanning tree algorithm.

Results. In a total area of 154 deg², we have detected 4061 candidate clusters at 3σ or above (6802 at 2σ and above), in the redshift range 0.1 ≤ z ≤ 1.15, with estimated mean masses between 1.3  × 10¹⁴ and 12.6  × 10¹⁴ M_⊙. This catalogue of candidate clusters will be available at the CDS. We compare our detections with those made in various CFHTLS analyses with other methods. By stacking a subsample of clusters, we show that this subsample has typical cluster characteristics (colour − magnitude relation, galaxy luminosity function). We also confirm that the cluster-cluster correlation function is comparable to the one obtained for other cluster surveys and analyse large-scale filamentary galaxy distributions.

Conclusions. We have increased the number of known optical high-redshift cluster candidates by a large factor, an important step towards obtaining reliable cluster counts to measure cosmological parameters. The clusters that we detect behave as expected if they are located at the intersection of filaments by which they are fed.