  In order to test for non-Gaussianities with respect to scale-dependencies we
use so-called surrogate maps, in which possible phase correlations of the
Fourier phases of the original WMAP data and simulations, respectively, are
destroyed by applying a shuffling scheme to the maps. A statistical comparison
of the original maps with the surrogate maps then allows to test for the
existence of higher order correlations in the original maps, also and
especially on well-defined Fourier modes. Using Minkowski functionals as an
image analysis technique we calculate the deviation between the original data
and 500 surrogates for different hemispheres in the sky and find ecliptic
hemispherical asymmetries between northern and southern ecliptic sky. We find
strong deviations from Gaussianity in the WMAP data when considering the low-l
range with l = [2,20]. The analysis technique of the scaling indices leads to a
slightly lower deviation. Although the underlying foreground reduction methods
of the maps differ from each other, we find similar results for the WMAP 7yr
ILC map and the WMAP 7yr (needlet-based) NILC map in the low-l range. Our
results point once more to a cosmological nature of the signal. For a higher l
range with l = [120,300] the results differ between the two image analysis
techniques and between the two maps which makes an intrinsic nature of the
signal on this l range less likely. When we decrease the size of the analysed
sky regions for the low-l study, we do not find signatures of NG in the
northern sky. In the south we find individual spots which show deviations from
Gaussianity. In addition, we investigate non-Gaussian CMB simulations that
depend on the f_NL parameter of the local type. These simulations cannot
account for the detected signatures on the low-l range.
