The Galactic interstellar medium has a preferred handedness of magnetic misalignment

TL;DR

This study investigates the origin of the parity-odd $TB$ polarization signal in Galactic dust emission, providing evidence that the observed signal is unlikely due to random fluctuations and suggesting a preferred handedness in magnetic misalignment.

Contribution

The paper demonstrates that the observed $TB$ signal cannot be explained by symmetric magnetic misalignments, indicating a possible parity-violating physics in the interstellar medium.

Findings

Planck data shows a >10 sigma tension with symmetric misalignment simulations.

Galactic filament misalignment likely has a preferred handedness.

Results challenge the assumption that $TB$ signals are purely due to statistical fluctuations.

Abstract

The Planck mission detected a positive correlation between the intensity ($T$) and $B$-mode polarization of the Galactic thermal dust emission. The $TB$ correlation is a parity-odd signal, whose statistical mean vanishes in models with mirror symmetry. Recent work has shown with strong evidence that local handedness of the misalignment between the dust filaments and the sky-projected magnetic field produces $TB$ signals. However, it remains unclear whether the observed global $TB$ signal is caused by statistical fluctuations of magnetic misalignment angles, or whether some parity-violating physics in the interstellar medium sets a preferred misalignment handedness. The present work aims to make a quantitative statement about how confidently the statistical-fluctuation interpretation is ruled out by filament-based simulations of polarized dust emission. We use the publicly available DUSTFILAMENTS code to simulate the dust emission from filaments whose magnetic misalignment angles are symmetrically randomized, and construct the probability density function of $\xi_{p}$, a weighted sum of $TB$ power spectrum. We find that Planck data has a $\gtrsim 10\sigma$ tension with the simulated $\xi_{p}$ distribution. Our results strongly support that the Galactic filament misalignment has a preferred handedness, whose physical origin is yet to be identified.