Cosmic shear statistics and cosmology

Abstract

Abstract. We report a measurement of cosmic shear correlations using an effective area of 6.5 deg 2 of the VIRMOS deep imaging survey in progress at the Canada-France-Hawaii Telescope. We measured various shear correlation functions, the aperture mass statistic and the top-hat smoothed variance of the shear with a detection significance exceeding 12 σ. We present results on angular scales from 3 arcsec to half a degree. The lensing origin of the signal is confirmed through tests that rely on the scalar nature of the gravitational potential. The different statistical measures give consistent results over the full range of angular scales. These important tests of the measurements demonstrate that the measured correlations could provide accurate constraints on cosmological parameters, subject to the systematic uncertainty in the source redshift distribution. The measurement over more than two decades of scale allows one to evaluate the effect of the shape of the power spectrum on cosmological parameter estimation. The degeneracy on σ8 − Ω0 can be broken if priors on the shape of the linear power spectrum (parameterized by Γ) are assumed. For instance, with Γ = 0.21 and at the 95% confidence level, we obtain 0.65 < σ8 < 1.2 and 0.22 < Ω0 < 0.55 for open models, and σ8 > 0.7 and Ω0 < 0.4 for flat (Λ-CDM) models. We discuss how these results would scale if the assumed source redshift distribution needed to be modified with forthcoming measurements of photometric redshifts. From the tangential/radial mode decomposition we can set an upper limit on the intrinsic shape alignment, which has recently been suggested as a possible contribution to the lensing signal. Within the error bars, there is no detection of intrinsic shape alignment for scales larger than 1 .

Observational probes of cosmic acceleration

“…Cosmic shear was finally detected in 2000 by several groups (Wittman et al, 2000;Bacon et al, 2000;Van Waerbeke et al, 2000), and in deeper but narrower data from HST (Rhodes et al, 2001;Refregier et al, 2002). Over the same period, several additional square degrees were observed with long exposure times in excellent seeing using ground-based telescopes (Van Waerbeke et al, 2001Bacon et al, 2003;Hamana et al, 2003). The first wide-shallow surveys were also carried out from the ground: the 53 deg 2 Red-Sequence Cluster Survey (Hoekstra et al, 2002) and the 75 deg 2 CTIO survey (Jarvis et al, 2003).…”

Analysis of two-point statistics of cosmic shear

“…The determination of ξ − on small angular scales is much more difficult than for ξ + , owing to the smallness of ξ − for small ϑ. Note that the noise scales like A −1/2 , so that from a survey of 16 sq deg, like the DESCART survey (see van Waerbeke et al 2001) one should be able to obtain reliable measurements of ξ + for ϑ < ∼ 1 • , and of ξ − for 10 < ∼ ϑ < ∼ 2 • in bins of relative width of 0.1. Fig.…”

“…In Fig. 4 of van Waerbeke et al (2002), the influence of the non-linear density evolution on the kurtosis of M ap was studied, using ray-tracing simulations through numerically generated cosmological matter distributions. The non-Gaussian effects start to become non-negligible for angular scales below ∼5 .…”

“…Cosmic shear, the distortion of the images of distant galaxies by the tidal gravitational field of intervening matter inhomogeneities, offers a direct way of probing the statistical properties of the large-scale (dark) matter distribution in the Universe, without making any assumption on the relation between dark and luminous matter (e.g., Blandford et al 1991;Miralda-Escude 1991;Kaiser 1992Kaiser , 1998Jain & Seljak 1997;Bernardeau et al 1997;Schneider et al 1998, hereafter SvWJK;van Waerbeke et al 1999;Bartelmann & Schneider 1999;Jain et al 2000;White & Hu 2000;see Mellier 1999 and for recent reviews). The first detections of cosmic shear on wide-field imaging data (Bacon et al 2000(Bacon et al , 2002Kaiser et al 2000;van Waerbeke et al 2000van Waerbeke et al , 2001van Waerbeke et al , 2002Wittman et al 2000;Maoli et al 2001;Rhodes et al 2001;Hämmerle et al 2002;Hoekstra et al 2002;Refregier et al 2002) has demonstrated the feasibility of this new window of observational cosmology, and yielded already the first constraints on cosmological parameters, most noticibly the normalization σ 8 of the dark matter power spectrum, but also on the matter density parameter Ω m Hoekstra et al 2002).…”

“…The first detections of cosmic shear on wide-field imaging data (Bacon et al 2000(Bacon et al , 2002Kaiser et al 2000;van Waerbeke et al 2000van Waerbeke et al , 2001van Waerbeke et al , 2002Wittman et al 2000;Maoli et al 2001;Rhodes et al 2001;Hämmerle et al 2002;Hoekstra et al 2002;Refregier et al 2002) has demonstrated the feasibility of this new window of observational cosmology, and yielded already the first constraints on cosmological parameters, most noticibly the normalization σ 8 of the dark matter power spectrum, but also on the matter density parameter Ω m Hoekstra et al 2002).…”