THE LIMITATIONS OF COSMIC-MICROWAVE-BACKGROUND MEASUREMENTS DUE TO LINEAR-POLARIZATION OF GALACTIC RADIO-EMISSION

In the light of the results of experiments measuring the absolute temp erature and the anisotropy of the cosmic microwave background, and con sidering the requirements for new experiments, we try to introduce som e considerations related to the polarized component of the galactic ra dio emission. The present knowledge in the polarization of galactic ra dio emission cannot exclude a priori that it may affect considerably t he results of cosmic microwave background measurements, not only those of polarization, as expected, but also low frequency spectral measure ments (nu less than or equal to 3 GHz) and anisotropy measurements (nu less than or equal to 50 GHz). In some particular instrumental config urations and depending on the frequency, the polarized component of ga lactic radio emission may be the major source of errors, especially in anisotropy and, of course, in polarization measurements. We conclude that part of cosmic microwave background experiments is seriously limi ted in sensitivity by this partially polarized foreground, and the sen sitivities actually required (about +/- 100 mK for spectral measuremen ts and Delta T/T congruent to 10(-5) for anisotropies) cannot be reach ed without taking that into account.