| Abstract: | The polarized thermal emission from Galactic dust is the main foreground
present in measurements of the polarization of the cosmic microwave background
(CMB) at frequencies above 100GHz. We exploit the Planck HFI polarization data
from 100 to 353GHz to measure the dust angular power spectra $C_ell^{EE,BB}$
over the range $40<ell<600$. These will bring new insights into interstellar
dust physics and a precise determination of the level of contamination for CMB
polarization experiments. We show that statistical properties of the emission
can be characterized over large fractions of the sky using $C_ell$. For the
dust, they are well described by power laws in $ell$ with exponents
$alpha^{EE,BB}=-2.42pm0.02$. The amplitudes of the polarization $C_ell$ vary
with the average brightness in a way similar to the intensity ones. The dust
polarization frequency dependence is consistent with modified blackbody
emission with $eta_d=1.59$ and $T_d=19.6$K. We find a systematic ratio
between the amplitudes of the Galactic $B$- and $E$-modes of 0.5. We show that
even in the faintest dust-emitting regions there are no "clean" windows where
primordial CMB $B$-mode polarization could be measured without subtraction of
dust emission. Finally, we investigate the level of dust polarization in the
BICEP2 experiment field. Extrapolation of the Planck 353GHz data to 150GHz
gives a dust power $ell(ell+1)C_ell^{BB}/(2pi)$ of
$1.32 imes10^{-2}mu$K$_{CMB}^2$ over the $40<ell<120$ range; the statistical
uncertainty is $pm0.29$ and there is an additional uncertainty (+0.28,-0.24)
from the extrapolation, both in the same units. This is the same magnitude as
reported by BICEP2 over this $ell$ range, which highlights the need for
assessment of the polarized dust signal. The present uncertainties will be
reduced through an ongoing, joint analysis of the Planck and BICEP2 data sets. |
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