GALACTIC DUST POLARIZED EMISSION AT HIGH-LATITUDES AND CMB POLARIZATION

With recent instrumental advances, it might become possible to measure the polarization of the Cosmic Microwave Background (CMB), e.g. by fu ture space missions like MAP and Planck Surveyor. In this paper, we es timate the dust polarized emission in our galaxy which is the major fo reground to cope with for measuring the CMB polarization in the Wien p art of CMB spectrum. We model the dust polarized emission in the galax y using the three-dimensional HI maps of the Leiden/Dwingeloo survey a t high galactic latitudes. We use the fact that the dust emission, for a wide range of wavelengths, has a tight correlation with the HI emis sion maps of this survey (Boulanger et al. 1996). Assuming the dust gr ains to be oblate with axis Patio similar or equal to 2/3, which recen t studies support, we determine the intrinsic dust polarized emissivit y. The distribution of magnetic field with respect to the dust grain d istribution is quite uncertain, we thus consider three extreme cases: (1) The magnetic held is aligned with the major axis of the dust struc ture, (2) the magnetic field has a random direction in the plane perpe ndicular to the direction of major axis of the dust structure, and (3) the magnetic field is unidirectional throughout. We further assume, a s recent observations and theoretical analyses support, that the dust grains align with the magnetic field independently of its strength. Th e polarization reduction factor from misalignment of the direction of polarization from the plane of the sky and the differential polarizati on along a line of sight is calculated using these maps, to construct two-dimensional maps of dust polarized emission. We calculate the angu lar power spectrum of dust polarized emission from these maps and cast it in variables which allow a direct comparison with the polarized co mponent of the CMB. Our results, at frequencies similar or equal to 10 0 GHz, suggest that: (a) This foreground contamination is smaller than the scalar-induced polarization of the CMB at rho greater than or sim ilar to 200 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 rho greater than or simil ar to 200, (b) the temperature-polarization cross correlation for dust emission is more than an order of magnitude below the CMB signal for rho greater than or equal to 200.