Dust-Polarization Maps for Local Interstellar Turbulence

We show that simulations of magnetohydrodynamic turbulence in the multiphase interstellar medium yield an $E/B$ ratio for polarized emission from Galactic dust in broad agreement with recent Planck measurements. In addition, the $B$-mode spectra display a scale dependence that is consistent with observations over the range of scales resolved in the simulations. The simulations present an opportunity to understand the physical origin of the $E/B$ ratio and a starting point for more refined models of Galactic emission of use for both current and future cosmic microwave background experiments.

Figure 1

Sample synthetic polarization maps for case $A$ corresponding to projections parallel (left) and perpendicular (right) to the mean field ${\mathit{b}}_0$. The drapery texture generated using the line integral convolution (LIC) technique [28] shows the POS magnetic field structure. Pseudovectors indicate the polarization direction (predominantly perpendicular to the field). Color shows the intensity in units of Hi column density. These maps are built on full-resolution numerical data smoothed with a low-pass boxcar filter of length 5 voxels, while no filtering is applied to compute the spectra.

Figure 2

Time-average $B$-mode spectra in arbitrary units (top) and $E/B$ spectral ratios (bottom) for case $A$ with strong large-scale magnetic field anisotropy (left) and less anisotropic case $B$ (right). Dotted line in the top panels shows least-squares fit for projection along the mean field. Horizontal dotted line in the bottom panels indicates $E/B\approx 1.92$ measured by Planck [25].