First cosmic shear results from the Canada-France-Hawaii Telescope Wide Synoptic Legacy Survey
H. Hoekstra, Y. Mellier, L. van Waerbeke, E. Semboloni, L. Fu, M. J. Hudson, L. C. Parker, I. Tereno, K. Benabed
TL;DR
First cosmic shear results from CFHTLS Wide demonstrate a robust E-mode signal with no significant B-mode, enabling constraints on the matter density $\Omega_m$ and the power-spectrum normalization $\sigma_8$ by comparing the observed top-hat shear variance to non-linear $P_\kappa(l)$. The analysis marginalizes over the Hubble parameter $h$ and the source redshift distribution, using a parameterized $n(z)$ with mean $\langle z\rangle\approx0.81$ and two non-linear prescriptions, $P_\kappa(l)$, to derive $\sigma_8$ values around $0.88\pm0.06$ (Peacock & Dodds) or $0.85\pm0.06$ (Smith et al.). The results are consistent with previous cosmic shear surveys and, when combined with Deep CFHTLS data, place a constraint $w_0<-0.8$ for a constant dark-energy equation of state. This work validates CFHTLS as a powerful platform for precision cosmology with cosmic shear and foreshadows tighter constraints with the full 140 deg$^2$ survey and photometric redshifts.
Abstract
We present the first measurements of the weak gravitational lensing signal induced by the large scale mass distribution 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 square degree in five filters. We have analysed ~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 marginalising over the Hubble parameter h=[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. 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.