| Abstract : | Accurate component separation of full-sky maps in the radio and microwave frequencies, such as the cosmic microwave background (CMB), relies on a thorough understanding of the statistical properties of the Galactic foreground emission. Using scalar Minkowski functionals (MFs) and their tensorial generalisation known as Minkowski tensors, we analyse the statistical properties of one of the major foreground components, namely the Galactic synchrotron. In this study, we use the all-sky Haslam 408 MHz synchrotron temperature map, WMAP and Planck synchrotron temperature and polarisation maps. We focus on understanding the nature of non-Gaussianity, statistical isotropy and filamentarity of the fluctuations at various sky regions and angular scales. These details are all important to improve the foreground modelling in the component separation pipelines. Our analysis on the Haslam map shows that the synchrotron field is highly non-Gaussian, and the overall non-Gaussianity decreases as we go to smaller angular scales. We find that the nature of non-Gaussianity is of kurtosis origin, and in the cooler regions of the field, non-Gaussianity can be expressed as a perturbative expansion. Our anisotropy analysis shows that the Haslam field is statistically isotropic in the regions away from the Galactic plane. This motivates us to explore the features of the synchrotron field at other frequency bands, given by WMAP and Planck in temperature and polarisation at 23 and 30 GHz, respectively. This multi-frequency analysis helps validate the assumptions taken in the synchrotron modelling and examine the efficiency of different component separation techniques used in WMAP and Planck. These steps are crucial to minimising residual contamination in the cleaned maps and capturing tiny cosmological signals such as CMB B-modes. |
