Mapping the large-angle deviation from Gaussianity in simulated CMB maps
  [Abridged] In recent works we have proposed two new large-angle
non-Gaussianity indicators based on skewness and kurtosis of patches of CMB
sky-sphere, and used them to find out significant deviation from Gaussianity in
frequency bands and foreground-reduced CMB maps. Simulated CMB maps with
assigned type and amplitude of primordial non-Gaussianity are important tools
to determine the strength, sensitivity and limitations of non-Gaussian
estimators. Here we investigate whether and to what extent our non-Gaussian
indicators have sensitivity to detect non-Gaussianity of local type,
particularly with amplitude within the seven-year WMAP bounds. We make a
systematic study by employing our statistical tools to generate maps of
skewness and kurtosis from several thousands of simulated maps equipped with
non-Gaussianity of local type of various amplitudes. We show that our
indicators can be used to detect large-angle local-type non-Gaussianity only
for relatively large values of the non-linear parameter $f_{\rm NL}^{\rm
local}$. Thus, our indicators have not enough sensitivity to detect deviation
from Gaussianity with the non-linear parameter within the seven-year WMAP
bounds. This result along with the outcomes of frequency bands and
foreground-reduced analyses suggest that non-Gaussianity captured in the
previous works by our indicators is not of primordial origin, although it might
have a primordial component. We have also made a comparative study of
non-Gaussianity of simulated maps and of the full-sky WMAP foreground-reduced
seven-year ILC-7yr map. An outcome of this analysis is that the level of
non-Gaussianity of ILC-7yr map is higher than that of the simulated maps for
$f_{\rm NL}^{\rm local}$ within WMAP bounds. This provides quantitative
indications on the suitability of the ILC-7yr map as a Gaussian reconstruction
of the full-sky CMB.
