Canada-France-Hawaii Telescope Legacy Survey Research Articles

Reconstruction of the One‐Point Distribution of Convergence from Weak Lensing by Large‐Scale Structure

Weak lensing measurements are starting to provide statistical maps of the distribution of matter in the universe that are increasingly precise and complementary to cosmic microwave background maps. The probability distribution (PDF) provides a powerful tool to test non-Gausian features in the convergence field and to discriminate the different cosmological models. In this letter, we present a new PDF space Wiener filter approach to reconstruct the probability density function of the convergence from the noisy convergence field. We find that for parameters comparable to the CFHT legacy survey, the averaged PDF of the convergence in a 3 degree field can be reconstructed with an uncertainty of about 10%, even though the pointwise PDF is noise dominated.

Joint cosmological parameters forecast from CFHTLS-cosmic shear and CMB data

We present a prospective analysis of a combined cosmic shear and cosmic microwave background data sets, focusing on a Canada France Hawaii Telescope Legacy Survey (CFHTLS) type lensing survey and the current WMAP-1 year and CBI data. We investigate the parameter degeneracies and error estimates of a seven parameter model, for the lensing alone as well as for the combined experiments. The analysis is performed using a Monte Carlo Markov Chain calculation, allowing for a more realistic estimate of errors and degeneracies than a Fisher matrix approach. After a detailed discussion of the relevant statistical techniques, the set of the most relevant 2 and 3-dimensional lensing contours are given. It is shown that the combined cosmic shear and CMB is particularly efficient to break some parameter degeneracies. The principal component directions are computed and it is found that the most orthogonal contours between the two experiments are for the parameter pairs , and , where ns and are, respectively, the slope of the primordial mass power spectrum and the running of the spectral index. It is shown, under the assumption of perfectely controlled systematics, that an improvement of a factor of 2 is expected on the running of the spectral index from the combined data sets. Forecasts for error improvements from a wide field space telescope lensing survey are also given.

Cosmological Constraints from Cosmic Shear and CMB

We analyse the sensitivity of cosmic shear 2-point statistics to the cosmological parameters, by using Monte Carlo Markov Chain (MCMC) methods. In particular, we investigate degeneracies among parameters and compare them to the CMB ones. Specializing on a Canada France Hawaii Telescope Legacy Survey (CFHTLS) type lensing survey and WMAP-1 year and CBI CMB data, we find cosmic shear information improves CMB cosmological parameters constraints by a factor of 1.5 – 2.5.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

Discovering and securing TNOs: the CFHTLS Ecliptic survey

We have developed an international collaboration aimed at discovering and long-term tracking of a large Trans-Neptunian Object (TNO) sample. The scientific rationale behind this extended observational effort is to understand the dynamical structure of the outer Solar System. This structure provides a unique tracer of planetary accretion processes and constrains models of formation and early evolution of our outer Solar System. Our observational program is designed to first discover a large sample of TNOs in well characterized surveys and then track them in a manner which will avoid what we call ‘follow-up bias’. We first briefly describe the current status of our current observational knowledge of the Kuiper Belt. Next we show how following-up almost all objects discovered in a survey has changed our view of the dynamical structure of the Kuiper Belt. Thanks to our work, previously empty places have been filled in, the relative importance of the then known dynamical population have been largely modified, and a new, potentially very large, population have been discovered. Discoveries presented in this paper were done at CFHT, while recoveries were performed on multiple telescopes, including in particular the ESO telescopes and the MPIA telescopes in Calar Alto (Spain). Finally, we briefly describe the ecliptic component of the CFHT Legacy Survey for which Kuiper Belt science is the main driver. Our experience with discovery and follow-up observations has led us to design an efficient time-sequence of observations for this survey. To cite this article: J.-M. Petit, B. Gladman, C. R. Physique 4 (2003).

Three-point correlations in weak lensing surveys: model predictions and applications

We use the halo model of clustering to compute two- and three-point correlation functions for weak lensing, and apply them in a new statistical technique to measure properties of massive haloes. We present analytical results on the eight shear three-point correlation functions constructed using a combination of the two shear components at each vertex of a triangle. We compare the amplitude and configuration dependence of the functions with ray-tracing simulations and find excellent agreement for different scales and models. These results are promising, since shear statistics are easier to measure than the convergence. In addition, the symmetry properties of the shear three-point functions provide a new and precise way of disentangling the lensing E mode from the B mode due to possible systematic errors. We develop an approach based on correlation functions to measure the properties of galaxy-group and cluster haloes from lensing surveys. Shear correlations on small scales arise from the lensing matter within haloes of mass M ? 10 1 3 M O .. Thus, the measurement of two- and three-point correlations can be used to extract information on halo density profiles, primarily the inner slope and halo concentration. We demonstrate the feasibility of such an analysis for forthcoming surveys. We include covariances in the correlation functions due to sample variance and intrinsic ellipticity noise to show that 10 per cent accuracy on profile parameters is achievable with surveys such as the CFHT Legacy survey, and significantly better with future surveys. Our statistical approach is complementary to the standard approach of identifying individual objects in survey data and measuring their properties. It can be extended to perform a combined analysis of the large-scale, perturbative regime down to small, subarcminute scales, to obtain consistent measurements of cosmological parameters and halo properties.