Galactic dust polarized emission at high latitudes and CMB polarization
S. Prunet, S. K. Sethi, F. R. Bouchet, M. A. Miville-Deschênes;
AaA, 1998, 339, 187
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 =~ 2/3, 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 =~ 100 GHz, suggest that: (a) This foreground
contamination is smaller than the scalar-induced polarization of the CMB at l ga 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 l ga 200, (b) the temperature-polarization cross
correlation for dust emission is more than an order of magnitude below the CMB signal
for l >= 200.
KEYWORDS: cosmic microwave background, polarization, ism: clouds, magnetic fields
PERSOKEY:polarisation, h_i, 21 cm, statistical analysis, cirrus, ,
CODE: prunet98