Can the observed E/B ratio for dust galactic foreground be explained by sub-Alfvenic turbulence?

TL;DR

This paper investigates whether sub-Alfvénic magnetohydrodynamic turbulence can explain the observed E/B polarization ratio in galactic dust, challenging previous models and supporting the applicability of MHD turbulence in the interstellar medium.

Contribution

It demonstrates that sub-Alfvénic MHD turbulence with low Alfvén Mach numbers can account for the observed E/B polarization ratio in galactic dust.

Findings

Sub-Alfvénic turbulence explains the E/B ratio.

High galactic latitude MHD turbulence is consistent with observations.

Challenges previous narrow-parameter models.

Abstract

Recent Planck observations of dust polarization in the Galaxy have revealed that the power in $E$ mode is twice that in $B$ mode. Caldwell et. al. have formulated a theoretical model in the context of magnetohydrodynamic (MHD) turbulence and found it problematic to account for this result. In particular, they concluded that there is a very narrow range of theoretical parameters that could account for the observation. This poses a problem of whether the accepted description of MHD turbulence can apply to the interstellar medium. We revisit the problem and demonstrate that MHD turbulence corresponding to the high galactic latitudes range of Alfv\'en Mach numbers, i.e. $M_A\lesssim 0.5$, can successfully explain the available results for the $E$ to $B$ mode ratio.