B5 - Weak lensing and constraints on the Dark Energy equation-of-state

Principal Investigators: T. Erben, P. Schneider (Bonn); St. Seitz (Munich)


Lensing by the large-scale structure is potentially the most promising empirical probe of the properties of Dark Energy, owing to its sensitivity to the expansion history of the Universe and the growth of large-scale structure. Major Dark Energy surveys employing the lensing technique are underway with strong involvements of our groups: after the successful conduction of the CFHTLenS survey project,the KiDS/VIKING and DES surveys will present the next breakthroughs in cosmic shear cosmology, with the ESA satellite mission Euclid already on the horizon. This proposal aims towards our strong participation in conducting and exploiting these new surveys, both of which surpass existing surveys in their combination of depth, area, spectral coverage and image quality by a large margin. As such, we expect both surveys to improve on current cosmological constraints from cosmic shear by a factor of about three, and to pave the way towards Euclid. The Munich group will concentrate on DES, of which it is a partner, whereas the Bonn group is major partner in a collaboration for the weak lensing analysis of KiDS/VIKING, responsible for the preparation of the optical data used for weak lensing, and capitalizing on the experience gained within CFHTLenS. The increased survey size, and its corresponding decrease of statistical errors, necessitates better control of systematics, allows for more sophisticated exploitation of the data (like higher-order statistical information), and requires new analysis tools. We will thus focus on key aspects for the successful analysis of these surveys: improving techniques for shape measurements on PSF-convolved noisy and pixelized images, developing practical methods for extracting the non-Gaussian part of the shear signal which contains independent information about the cosmological mass distribution, and methods for data compression, required for realistic covariance estimates and thus for proper cosmological analysis. The studies carried out in B5 are driven by the requirement to be able to analyze and interpret weak lensing shear surveys in order to derive Dark Energy constraints. Our effort results in a substantial benefit also for other galaxy cluster-centered TR33 sub-projects: we do not only develop shape measurement pipelines for cosmic shear studies, but also participate in challenges measuring gravitational shear in the cluster regime, and we also propagate shape measurement errors into mass estimate and NFW-profile parameter errors.