| Abstract
| - Aims. We present for the first time a coherent model of the polarized Galactic synchrotron and thermal dust emissions that are likely to form the predominant diffuse foregrounds for measuring the polarized CMB fluctuations by the P lanck satellite mission. Methods. We produced 3D models of the Galactic magnetic field including regular and turbulent components, and of the distribution of matter in the Galaxy including relativistic electron and dust grain components. By integrating along the line of sight, we constructed maps of the polarized Galactic synchrotron and thermal dust emission for each of these models and compared them to currently available data. We consider the 408 MHz all-sky continuum survey, the 23 GHz band of the Wilkinson Microwave Anisotropy Probe, and the 353 GHz A rcheops data. Results. The best-fit parameters obtained are consistent with previous estimates in the literature based only on synchrotron emission and pulsar rotation measurements and this allows us to reproduce the large-scale features observed in the data. Unmodeled local Galactic structures and the effect of turbulence make it difficult to accurately reconstruct observations in the Galactic plane. Conclusions. Finally, using the best-fit model we are able to estimate the expected polarized foreground contamination at the P lanck frequency bands. For the CMB bands, 70, 100, 143 and 217 GHz, at high Galactic latitudes although the CMB signal dominates in general, a significant foreground contribution is expected at large angular scales. In particular, this contribution will dominate the CMB signal for the B modes expected from realistic models of a background of primordial gravitational waves.
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