Determine the three-dimensional magnetic-field structure governing cosmic-ray electron transport

Determine the small-scale and three-dimensional magnetic-field structure of NGC 2442, including any component perpendicular to the galactic disk, to establish more accurate constraints on cosmic-ray electron propagation to the synchrotron island.

Background

The simulations model cosmic-ray electron transport in a prescribed two-dimensional magnetic field whose field lines follow the spiral-arm structure. The authors find that anisotropic diffusion can transport electrons to the island more efficiently than isotropic diffusion, but they note that the assumed field geometry is limited by the available polarimetric observations, especially because Faraday depolarization affects the low-frequency data.

The unresolved small-scale field structure and the omission of a vertical magnetic-field component could materially affect the predicted transport paths and diffusion efficiency. A realistic three-dimensional field model would therefore provide tighter constraints on the origin and propagation of the island’s cosmic-ray electrons.

References

However, because of the limitations of current polarimetric observations, especially the strong Faraday depolarization affecting low-frequency L-band data, we are unable to constrain the small-scale magnetic-field distribution, which would also affect CR transport. Moreover, a more realistic 3D magnetic-field model should provide tighter constraints on CRE propagation.

— Cosmic-ray electron propagation in the peculiar barred spiral galaxy NGC 2442  (2609.10270 - Wang et al., 9 Sep 2026) in Section 4.1, “2D CRE propagation simulation in NGC 2442”