The multiphase interstellar medium as a common origin for magnetic misalignment and TB parity violation

TL;DR

This study links magnetic field misalignments and TB parity violations in the Galactic interstellar medium to large-scale multiphase gas structures, offering a new physical model supported by Planck and starlight polarization data.

Contribution

It introduces a multiphase, geometrical model explaining the origin of magnetic misalignment and TB parity violation as projection effects from large-scale gas structures in the ISM.

Findings

Both effects are prominent at large angular scales (≥10°) with stronger signals in the northern hemisphere.

The model explains the observables without requiring small-scale filament misalignments.

Planck polarization data support the multiphase, geometrical interpretation.

Abstract

We present an original data analysis and a physical model that provide new insights into the origin of, and relationship between, two observables of the dusty, polarized Galaxy at intermediate and high latitudes: (i) the misalignment between HI filamentary structures and magnetic fields and (ii) the positive $TB$ correlation measured in Planck data suggesting parity violation in the interstellar medium (ISM). We confirm an observational link between the two effects and find that both are predominantly produced at large angular scales ($\geq 10^\circ$, multipoles $\ell \leq 20$) with a significantly stronger signal in the northern hemisphere. We propose a model in which filaments and magnetic fields appear misaligned in projection because they are sourced by cold and warm gas phases distributed in different proportions in the Solar neighborhood, from the wall of the Local Bubble to larger distances. These projection effects at large angular scales can produce coherent signatures that propagate to smaller scales in power spectra without invoking local, small-scale filament misalignment. Within this frame, HI filaments remain statistically aligned with the magnetic field in 3D, although with a projected scatter of tens of degrees that requires further investigation. The multiphase, geometrical model presented in this work is supported by Planck polarization data at 30 GHz, where synchrotron radiation dominates, and at 217 and 353 GHz, where dust emission dominates. Our analysis also incorporates starlight polarization measurements. The model introduced here suggests a new interpretation of two unexplained observables and emphasizes the role of the large-scale magnetized ISM in shaping polarized Galactic emission, which has important implications for both Galactic astrophysics and cosmological foreground characterization.