Dark-energy constraints and correlations with systematicsfrom CFHTLS weak lensing, SNLS supernovae Ia and WMAP5

摘要

Aims. We combine measurements of weak gravitational lensing from the CFHTLS-Wide survey, supernovae Ia from CFHT SNLS andCMB 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 cosmologicalparameters.Methods. We implemented an MCMC algorithm to sample the parameter space of a flat CDM model with a dark-energy componentof constant w. Systematics in the data are parametrised and included in the analysis. We determine the influence of photometriccalibration of SNIa data on cosmological results by calculating the response of the distance modulus to photometric zero-pointvariations. The weak lensing data set is tested for anomalous field-to-field variations and a systematic shape measurement bias forhigh-redshift galaxies.Results. Ignoring photometric uncertainties for SNLS biases cosmological parameters by at most 20 of the statistical errors, usingsupernovae 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 underestimationof the lensing signal, the normalisation 0-8 increases by up to 8. Combining all three probes we obtain —0.10 < 1 + w < 0.06 at68 confidence (-0.18 < 1+w < 0.12 at 95), including systematic errors. Our results are therefore consistent with the cosmologicalconstant A. Systematics in the data increase the error bars by up to 35; the best-fit values change by less than 0.15(r.