The non-Gaussian tail of cosmic-shear statistics

Owing to gravitational instability, an initially Gaussian density field dev elops non-Gaussian features as the Universe evolves. The most prominent non -Gaussian features are massive haloes, visible as clusters of galaxies. The distortion of high-redshift galaxy images because of the tidal gravitation al field of the large-scale matter distribution, called cosmic shear, can b e used to investigate the statistical properties of the large-scale structu re (LSS). In particular, non-Gaussian properties of the LSS will lead to a non-Gaussian distribution of cosmic-shear statistic. The aperture mass (M-a p) statistics, recently introduced as a measure for cosmic shear, is partic ularly well suited for measuring these non-Gaussian properties. In this pap er we calculate the highly non-Gaussian tail of the aperture mass probabili ty distribution, assuming Press-Schechter theory for the halo abundance and the 'universal' density profile of haloes as obtained from numerical simul ations. We find that for values of M-ap much larger than its dispersion, th is probability distribution is closely approximated by an exponential, rath er than a Gaussian. We determine the amplitude and shape of this exponentia l for various cosmological models and aperture sizes, and show that wide-fi eld imaging surveys can be used to distinguish between some of the currentl y most popular cosmogonies. Our study here is complementary to earlier cosm ic-shear investigations, which focused more on two- and three-point statist ical properties.