Dark-energy constraints and correlations with systematics from CFHTLS weak lensing, SNLS supernovae Ia and WMAP5^*

¹ Institut d'Astrophysique de Paris, CNRS UMR 7095 & UPMC, 98bis boulevard Arago, 75014 Paris, France e-mail: kilbinger@iap.fr
² LPNHE, CNRS-IN2P3 and Universités Paris VI & VII, 4 place Jussieu, 75252 Paris Cedex 05, France
³ Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
⁴ INAF – Osservatorio Astronomico di Capodimonte, via Moiariello 16, 80131 Napoli, Italy
⁵ Shanghai Key Lab for Astrophysics, Shanghai Normal University, Shanghai 200234, PR China
⁶ CEREMADE, Université Paris Dauphine, 75775 Paris Cedex 16, France
⁷ National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, Japan
⁸ Observatoire de Besançon, 41bis avenue de l'Observatoire, BP 1615, 25010 Besançon Cedex, France
⁹ Research Institute for Information Technology, University of Kyushu 6-10-1 Hakozaki, Higashi-ward, Fukuoka 812-8581, Japan

Received: 28 October 2008
Accepted: 18 January 2009

Abstract

Aims. We combine measurements of weak gravitational lensing from the CFHTLS-Wide survey, supernovae Ia from CFHT SNLS and CMB anisotropies from WMAP5 to obtain joint constraints on cosmological parameters, in particular, the dark-energy equation-of-state parameter w. We assess the influence of systematics in the data on the results and look for possible correlations with cosmological parameters.

Methods. We implemented an MCMC algorithm to sample the parameter space of a flat CDM model with a dark-energy component of constant w. Systematics in the data are parametrised and included in the analysis. We determine the influence of photometric calibration of SNIa data on cosmological results by calculating the response of the distance modulus to photometric zero-point variations. The weak lensing data set is tested for anomalous field-to-field variations and a systematic shape measurement bias for high-redshift galaxies.

Results. Ignoring photometric uncertainties for SNLS biases cosmological parameters by at most 20% of the statistical errors, using supernovae alone; the parameter uncertainties are underestimated by 10%. The weak-lensing field-to-field variance between 1 deg²-MegaCam pointings is 5-15% higher than predicted from N-body simulations. We find no bias in the lensing signal at high redshift, within the framework of a simple model, and marginalising over cosmological parameters. Assuming a systematic underestimation of the lensing signal, the normalisation  increases by up to 8%. Combining all three probes we obtain at 68% confidence ( at 95%), including systematic errors. Our results are therefore consistent with the cosmological constant Λ. Systematics in the data increase the error bars by up to 35%; the best-fit values change by less than 0.15σ.