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Foregrounds Unfortunately, the CMB is not the only source of polarized microwaves. While the atmosphere should be completely unpolarized, Galactic synchrotron radiation, interstellar dust emission and extragalactic point sources produce polarized signals that can contaminate measurements of the cosmological polarization. There is little experimental information on these polarized foregrounds, and no data at all on the angular scales and frequencies relevant for CMB experiments. Rough estimates of the foregrounds must therefore be extrapolated from other frequencies using their (still somewhat uncertain) spectra (see the full thesis for details). These estimates, illustrated in Figure 1.10, suggest that synchrotron radiation is the strongest source of polarized microwaves at frequencies below 50 GHz, while for frequencies above 200 GHz dust emission is dominant. Between these two frequencies is a window where the cosmological polarization can (hopefully) be measured with relatively little foreground contamination (The location of this window is relatively insensitive to uncertainties in the normalization of the foreground spectra, see Tegmark et. al. 1999).
Figure 1.9: Summary of the physics behind the structure of the CMB
Figure 1.10: Polarized foregrounds on sub-degree angular scales The Origin of Cosmological Polarization The Structure of Cosmological Polarization Power Spectra and the Structure of CMB Anisotropies Initial Conditions and Inflation The Evolution of Perturbations and Acoustic Oscillations Acoustic Oscillations and Apparent Temperature Variations |
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