First Cosmic Shear Results from the Canada-France-Hawaii Telescope Wide Synoptic Legacy Survey^*

We present the first measurements of the weak gravitational lensing signal induced by the large-scale mass distribution in the universe from data obtained as part of the ongoing Canada-France-Hawaii Telescope Legacy Survey (CFHTLS). The data used in this analysis are from the Wide Synoptic Survey, which aims to image ~170 deg² in five filters. We have analyzed an effective area of ~22 deg² (31 pointings) of i' data spread over two of the three survey fields. These data are of excellent quality, and the results bode well for the remainder of the survey: we do not detect a significant "B" mode, suggesting that residual systematics are negligible at the current level of accuracy. Assuming a cold dark matter model and marginalizing over the Hubble parameter h ∈ [0.6, 0.8], the source redshift distribution, and systematics, we constrain σ₈, the amplitude of the matter power spectrum. At a fiducial matter density Ω_m = 0.3 we find σ₈ = 0.85 ± 0.06. This estimate is in excellent agreement with previous studies. A combination of our results with those from the Deep component of the CFHTLS enables us to place a constraint on a constant equation of state for the dark energy, based on cosmic shear data alone. We find that w₀ < -0.8 at 68% confidence.