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Astron. Astrophys. 339, 187-193 (1998)


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Galactic dust polarized emission at high latitudes and CMB polarization

S. Prunet 1, S.K. Sethi 2, F.R. Bouchet 2 and M.-A. Miville-Deschênes 1

1 Institut d'Astrophysique Spatiale, Université Paris-Sud, F-91405 Orsay, France
2 Institut d'Astrophysique de Paris, 98 bis boulevard Arago, F-75014 Paris, France

Received 15 January 1998 / Accepted 31 July 1998

Abstract

With recent instrumental advances, it might become possible to measure the polarization of the Cosmic Microwave Background (CMB), e.g. by future space missions like MAP and Planck Surveyor. In this paper, we estimate the dust polarized emission in our galaxy which is the major foreground to cope with for measuring the CMB polarization in the Wien part of CMB spectrum. We model the dust polarized emission in the galaxy using the three-dimensional HI maps of the Leiden/Dwingeloo survey at high galactic latitudes. We use the fact that the dust emission, for a wide range of wavelengths, has a tight correlation with the HI emission maps of this survey (Boulanger et al. 1996). Assuming the dust grains to be oblate with axis ratio [FORMULA], which recent studies support, we determine the intrinsic dust polarized emissivity. The distribution of magnetic field with respect to the dust grain distribution is quite uncertain, we thus consider three extreme cases: (1) The magnetic field is aligned with the major axis of the dust structure, (2) the magnetic field has a random direction in the plane perpendicular to the direction of major axis of the dust structure, and (3) the magnetic field is unidirectional throughout. We further assume, as recent observations and theoretical analyses support, that the dust grains align with the magnetic field independently of its strength. The polarization reduction factor from misalignment of the direction of polarization from the plane of the sky and the differential polarization along a line of sight is calculated using these maps, to construct two-dimensional maps of dust polarized emission. We calculate the angular power spectrum of dust polarized emission from these maps and cast it in variables which allow a direct comparison with the polarized component of the CMB. Our results, at frequencies [FORMULA], suggest that: (a) This foreground contamination is smaller than the scalar-induced polarization of the CMB at [FORMULA] while the tensor-induced polarization of CMB, which is an order of magnitude smaller than the scalar-induced polarization, lies below the foreground contamination level for [FORMULA], (b) the temperature-polarization cross correlation for dust emission is more than an order of magnitude below the CMB signal for [FORMULA].

Key words: cosmic microwave background – polarization – ISM: clouds – magnetic fields

Send offprint requests to: S. Prunet

© European Southern Observatory (ESO) 1998

Online publication: September 30, 1998

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