Astronomy & Astrophysics

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Issue		A&A Volume 479, Number 1, February III 2008
Page(s)		9 - 25
Section		Cosmology (including clusters of galaxies)
DOI		10.1051/0004-6361:20078522

A&A 479, 9-25 (2008)
DOI: 10.1051/0004-6361:20078522

Very weak lensing in the CFHTLS wide: cosmology from cosmic shear in the linear regime

L. Fu^{1, 2}, E. Semboloni^{1, 3}, H. Hoekstra⁴, M. Kilbinger^{1, 3}, L. van Waerbeke⁵, I. Tereno^{1, 3}, Y. Mellier¹, C. Heymans^{1, 5}, J. Coupon¹, K. Benabed¹, J. Benjamin⁵, E. Bertin¹, O. Doré⁶, M. J. Hudson⁷, O. Ilbert^{8, 9}, R. Maoli^{1, 10}, C. Marmo¹, H. J. McCracken¹, and B. Ménard⁶

¹ Institut d'Astrophysique de Paris, UMR7095 CNRS, Université Pierre & Marie Curie, 98 bis boulevard Arago, 75014 Paris, France
e-mail: fu@iap.fr
² Shanghai Normal University, 100 Guilin RD, Shanghai 200234, PR China
³ Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
⁴ Department of Physics and Astronomy, University of Victoria, Victoria, B.C. V8P 5C2, Canada
⁵ University of British Columbia, Department of Physics and Astronomy, 6224 Agricultural Road, Vancouver, B.C. V6T 1Z1, Canada
⁶ Canadian Institute for Theoretical Astrophysics, University of Toronto 60 St. George Street Toronto, Ontario, M5S 3H8, Canada
⁷ Department of Physics and Astronomy, University of Waterloo, Waterloo ON N2L 3G1, Canada
⁸ Laboratoire d'Astrophysique de Marseille, UMR 6110 CNRS-Université de Provence, BP 8, 13376 Marseille Cedex 12, France
⁹ Institute for Astronomy, 2680 Woodlawn Drive, Honolulu, HI 96822-1897, USA
¹⁰ Department of Physics, University La Sapienza, Pl. A. Moro 2, 00185 Roma, Italy

(Received 21 August 2007 / Accepted 27 November 2007)

Abstract
Aims.We present an exploration of weak lensing by large-scale structure in the linear regime, using the third-year (T0003) CFHTLS Wide data release. Our results place tight constraints on the scaling of the amplitude of the matter power spectrum $\sigma_8$ with the matter density $\Omega_{\rm m}$ .
Methods.Spanning 57 square degrees to $i^{\prime}_ = 24.5$ over three independent fields, the unprecedented contiguous area of this survey permits high signal-to-noise measurements of two-point shear statistics from 1 arcmin to 4 degrees. Understanding systematic errors in our analysis is vital in interpreting the results. We therefore demonstrate the percent-level accuracy of our method using STEP simulations, an E/B-mode decomposition of the data, and the star-galaxy cross correlation function. We also present a thorough analysis of the galaxy redshift distribution using redshift data from the CFHTLS T0003 Deep fields that probe the same spatial regions as the Wide fields.
Results.We find $\sigma_8(\Omega_{\rm m} / 0.25)^ = 0.785$ $\pm$ 0.043 using the aperture-mass statistic for the full range of angular scales for an assumed flat cosmology, in excellent agreement with WMAP3 constraints. The largest physical scale probed by our analysis is 85 Mpc, assuming a mean redshift of lenses of 0.5 and a $\Lambda$ CDM cosmology. This allows for the first time to constrain cosmology using only cosmic shear measurements in the linear regime. Using only angular scales $\theta> 85$ arcmin, we find $\sigma_8(\Omega_{\rm m} / 0.25)_{{\rm lin}}^ = 0.837$ $\pm$ 0.084, which agree with the results from our full analysis. Combining our results with data from WMAP3, we find $\Omega_{\rm m}=0.248$ $\pm$ 0.019 and $\sigma_8=0.771$ $\pm$ 0.029.

Key words: gravitational lensing -- cosmological parameters -- cosmology: observations -- large-scale structure of Universe

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