A Multifrequency Analysis of the Polarized Diffuse Galactic Radio Emission at Degree Scales

Abstract

The polarized diffuse Galactic radio emission, mainly synchrotron emission, is expected to be one of the most relevant source of astrophysical contamination at low and moderate multipoles in cosmic microwave background polarization anisotropy experiments at frequencies lower then 50 to 100 GHz. We present here preliminary results based on a recent analysis of the Leiden surveys covering about 50% of the sky at low as well as at middle and high Galactic latitudes. By implementing specific interpolation methods to deal with these data, which show a large variation of the sampling across the sky, we produce maps of the polarized diffuse Galactic synchrotron component at frequencies between 408 and 1411 MHz with pixel sizes larger or equal to about 0.92 degrees. We derive the angular power spectrum of this component for the whole covered region and for three patches in the sky significantly oversampled with respect to the average and at different Galactic latitudes. We find multipole spectral indices typically ranging between about -3 and about -1, according to the considered frequency and sky region. At frequencies higher or equal to 610 MHz, the frequency spectral indices observed in the considered sky regions are about -3.5, compatible with an intrinsic frequency spectral index of about -5.8 and a depolarization due to Faraday rotation with a rotation measure RM of about 15 radians per square meter. This implies that the observed angular power spectrum of the polarized signal is about 85% or 20% of the intrinsic one at 1411 MHz or 820 MHz respectively.