Probing non-Gaussianities in the CMB with Minkowski Functionals and Scaling Indices using surrogates

We are analysing the cosmic microwave background (CMB) in respect to possible higher order correlations (HOCs) which would be indicators for non-Gaussianities in the primordial density field of the universe. Here, the analysis of the CMB Fourier phases is a promising and cosmological-model independent method. For generating so-called surrogate maps possible phase correlations of the Fourier phases of the original data (here the CMB map from the WMAP experiment) are destroyed applying a shuffling scheme to the maps in Fourier space. A comparison of the original maps and the surrogate maps then allows to test for the presence of HOCs in the original maps, also and especially on well-defined scales. Using Minkowski Functionals and Scaling Indices as test statistics for the HOCs in the maps we find deviations from the hypothesis of a Gaussian CMB with a significance of up to 10 sigma on largest scales, namely within the Fourier modes l from 0 to 20. We calculate the significance between the test statistics of the original data and the surrogates for different hemispheres in the sky and find hemispherical asymmetries as well as deviations from Gaussianity in the northern and southern sky. Calculating the significance for smaller parts of the sky enables us to locate certain regions in the southern sky that show deviations from Gaussianity while the signal found in the north vanishes.