Issue |
A&A
Volume 500, Number 3, June IV 2009
|
|
---|---|---|
Page(s) | 981 - 998 | |
Section | Cosmology (including clusters of galaxies) | |
DOI | https://doi.org/10.1051/0004-6361/200811413 | |
Published online | 29 April 2009 |
Photometric redshifts for the CFHTLS T0004 deep and wide fields*
1
Institut d'Astrophysique de Paris, UMR 7095 CNRS, Université Pierre et Marie Curie, 98bis boulevard Arago, 75014 Paris, France e-mail: coupon@iap.fr
2
Institute for Astronomy, 2680 Woodlawn Dr., University of Hawaii, Honolulu, Hawaii, 96822, USA
3
Canada-France-Hawaii telescope, 65-1238 Mamalahoa Highway, Kamuela, HI 9674, USA
4
Observatoire des Sciences de l'Univers de Besançon, UMR 6213 CNRS, 41bis avenue de l'Observatoire, 25010 Besançon, France
5
Laboratoire d'Astrophysique de Marseille (UMR 6110), CNRS-Université de Provence, 38 rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France
6
INAF-Osservatorio Astronomico di Brera, via Bianchi 46, 23807 Merate (LC), Italy
7
Osservatorio Astronomicoq di Bologna, via Ranzani 1, 40127 Bologna, Italy
8
IRA-INAF, via Gobetti, 101, 40129 Bologna, Italy
9
Service d'Astrophysique, CEA-Saclay, 91191 Gif-sur-Yvette, France
Received:
25
November
2008
Accepted:
8
April
2009
Aims. We compute photometric redshifts in the fourth public release
of the Canada-France-Hawaii Telescope Legacy Survey. This
unique multi-colour catalogue comprises
photometry in four deep fields of 1 deg2 each and
35 deg2 distributed over three wide fields.
Methods. We used a template-fitting method to compute photometric redshifts calibrated with a large catalogue of 16 983 high-quality spectroscopic redshifts from the VVDS-F02, VVDS-F22, DEEP2, and the zCOSMOS surveys. The method includes correction of systematic offsets, template adaptation, and the use of priors. We also separated stars from galaxies using both size and colour information.
Results. Comparing with galaxy spectroscopic redshifts, we find a photometric
redshift dispersion, ,
of 0.028–0.30 and an outlier rate,
, of
3–4% in the deep field at
< 24. In the wide
fields, we find a dispersion
of 0.037–0.039 and an outlier rate of 3–4% at
< 22.5.
Beyond
= 22.5 in the wide fields the number of outliers
rises from 5% to 10% at
< 23 and
< 24,
respectively. For the wide sample the systematic
redshift bias stays below 1% to
< 22.5, whereas
we find no significant bias in the deep fields.
We
investigated the effect of tile-to-tile photometric
variations and demonstrated that the accuracy of our
photometric redshifts is reduced by at most 21%.
Application of our star-galaxy classifier reduced
the contamination by stars in our catalogues from 60%
to 8% at
< 22.5 in our field with the highest
stellar density while keeping a complete galaxy sample. Our
CFHTLS T0004 photometric redshifts are distributed to the
community. Our release includes 592891 (
< 22.5)
and 244701 (
< 24) reliable galaxy photometric
redshifts in the wide and deep fields, respectively.
Key words: galaxies: distances and redshifts / cosmology: observations / cosmology: large-scale structure of Universe
Based on observations obtained with MegaPrime/MegaCam, a joint project of CFHT and CEA/DAPNIA, at the Canada-France-Hawaii Telescope (CFHT) which is operated by the National Research Council (NRC) of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientifique (CNRS) of France, and the University of Hawaii. This work is based in part on data products produced at Terapix and the Canadian Astronomy Data Centre as part of the Canada-France-Hawaii Telescope Legacy Survey, a collaborative project of NRC and CNRS.
© ESO, 2009
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