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Abstract: The Planck satellite will map the full sky at nine frequencies from 30 to 857GHz. The CMB intensity and polarization that are its prime targets arecontaminated by foreground emission. The goal of this paper is to compareproposed methods for separating CMB from foregrounds based on their differentspectral and spatial characteristics, and to separate the foregrounds intocomponents of different physical origin. A component separation challenge hasbeen organized, based on a set of realistically complex simulations of skyemission. Several methods including those based on internal templatesubtraction, maximum entropy method, parametric method, spatial and harmoniccross correlation methods, and independent component analysis have been tested.Different methods proved to be effective in cleaning the CMB maps fromforeground contamination, in reconstructing maps of diffuse Galactic emissions,and in detecting point sources and thermal Sunyaev-Zeldovich signals. The powerspectrum of the residuals is, on the largest scales, four orders of magnitudelower than that of the input Galaxy power spectrum at the foreground minimum.The CMB power spectrum was accurately recovered up to the sixth acoustic peak.The point source detection limit reaches 100 mJy, and about 2300 clusters aredetected via the thermal SZ effect on two thirds of the sky. We have found thatno single method performs best for all scientific objectives. We foresee thatthe final component separation pipeline for Planck will involve a combinationof methods and iterations between processing steps targeted at differentobjectives such as diffuse component separation, spectral estimation andcompact source extraction.

Author: S.M.Leach, J.-F.Cardoso, C.Baccigalupi, R.B.Barreiro, M.Betoule, J.Bobin, A.Bonaldi, J.Delabrouille, Zotti, C.Dickinson, H.K


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