S E M I N A R IDepartament d'Astronomia i Astrofísica
Universitat de València
Statistical analyses of Galactic radio surveys
INAF-IASF Bologna, Italia
Seminari del departament d'Astronomia i Astrofísica
Dijous 27 octubre 2005
Radio surveys at frequencies about 1 GHz allow to map the synchrotron emission in a frequency range where (possibly, except for very low Galactic latitutes or towards localized regions) it dominates over other radio components, mainly the free-free emission. In addition, an accurate modelling and subtraction of the Galactic foreground is necessary to map the intrinsic CMB anisotropies. The Leiden polarization surveys represent a unique opportunity for a radio multifrequency study of the Galactic synchrotron emission on large sky areas. I`ll present here the main results of a recent re-analysis of these surveys in terms of angular power spectrum that allows to focus on Faraday depolarization effects. In fact, they seem to be crucial for the understanding of the relative amplitudes and the different slopes of the angular power spectra at different frequencies. New total intensity and polarization data at 1.4 GHz have been recently accumulated over the whole sky. I`ll present here a statistical analysis of the corresponding maps. After a discussion on a dedicated point source subtraction, I`ll focus on the correlation properties of the Galactic radio emission described in terms of angular power spectrum on the whole sky, on large sky areas, and on small patches and present the distribution over the sky of the parameters (slope and amplitude) describing the power spectrum. The correlation with the Galactic emission properties at other radio frequencies is discussed. Finally, I`ll estimate the level of contamination expected at millimetre wavelengths, relevant for CMB anisotropy projects.