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

¹ LUX, Observatoire de Paris, Université PSL, Sorbonne Université, CNRS, 75014 Paris, France
² INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, 50125 Firenze, Italy
³ Laboratoire de Physique de l'Ecole Normale Supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université de Paris, 75005 Paris, France
⁴ Department of Physics, California Institute of Technology, Pasadena, CA 91125, USA
⁵ TAPIR, California Institute of Technology, MC 350-17, Pasadena, CA 91125, USA

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 12 December 2025
Accepted: 21 May 2026

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 T B 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 (≥10°, multipoles ℓ ≤ 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, H I 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.