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 similar to 170 deg(2) in five filters. We have analyzed an effective area of similar to 22 deg(2) (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(2) [0.6; 0.8], the source redshift distribution, and systematics, we constrain sigma(8), the amplitude of the matter power spectrum. At a fiducial matter density Omega(m) = 0.3 we find sigma(8) = 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 w(0) < -0.8 at 68% confidence.