Skewness and Kurtosis as Indicators of Non-Gaussianity in Galactic Foreground Maps

Observational cosmology is entering an era in which high precision will be required in both measurement and data analysis. Accuracy, however, can only be achieved with a thorough understanding of potential sources of contamination from foreground effects. Our primary focus will be on non- Gaussian effects in foregrounds. This issue will be crucial for coming experiments to determine B-mode polarization. We propose a novel method for investigating a data set in terms of skewness and kurtosis in locally defined regions that collectively cover the entire sky. The method is demonstrated on two sky maps: (i) the SMICA map of Cosmic Microwave Background fluctuations provided by the Planck Collaboration and (ii) a version of the Haslam map at 408 MHz that describes synchrotron radiation. We find that skewness and kurtosis can be evaluated in combination to reveal local physical information. In the present case, we demonstrate that the local properties of both maps are predominantly Gaussian. This result was expected for the SMICA map; that it also applies for the Haslam map is surprising. The approach described here has a generality and flexibility that should make it useful in a variety of astrophysical and cosmological contexts.