Cosmological parameters from combined second- and third-order aperture mass statistics of cosmic shear

Abstract

We present predictions for cosmological parameter constraints from combined measurements of second- and third-order statistics of cosmic shear. We define the generalized third-order aperture mass statistics <M_ap^3> and show that it contains much more information about the bispectrum of the projected matter density than the skewness of the aperture mass. From theoretical models as well as from LCDM ray-tracing simulations, we calculate <M_ap^2> and <M_ap^3> and their dependence on cosmological parameters. The covariances including shot noise and cosmic variance of M_ap^2, M_ap^3 and their cross-correlation are calculated using ray-tracing simulations. We perform an extensive Fisher matrix analysis, and for various combinations of cosmological parameters, we predict 1-sigma-errors corresponding to measurements from a deep 29 square degree cosmic shear survey. Although the parameter degeneracies can not be lifted completely, the (linear) combination of second- and third-order aperture mass statistics reduces the errors significantly. The strong degeneracy between Omega_m and sigma_8, present for all second-order cosmic shear measures, is diminished substantially, whereas less improvement is found for the near-degenerate pair consisting of the shape parameter Gamma and the spectral index n_s. Uncertainties in the source galaxy redshift z_0 increase the errors of all other parameters.