HI filaments as potential compass needles? Comparing the magnetic field structure of the Small Magellanic Cloud to the orientation of GASKAP-HI filaments

TL;DR

This study investigates the magnetic alignment of large-scale HI filaments in the Small Magellanic Cloud using ASKAP data, revealing preferential alignment with magnetic fields in certain regions and suggesting large-scale magnetic influence beyond the Milky Way.

Contribution

It introduces a novel combination of RHT and ray-tracing algorithms to analyze HI filament alignment with magnetic fields in the SMC, extending understanding of magnetic structures in external galaxies.

Findings

HI filaments in the SMC are aligned with magnetic fields in specific regions.

Large-scale magnetic alignment of HI filaments is observed outside the Milky Way.

Maps of filament orientations reveal complex gas dynamics influenced by multiple processes.

Abstract

High-spatial-resolution HI observations have led to the realisation that the nearby (within few hundreds of parsecs) Galactic atomic filamentary structures are aligned with the ambient magnetic field. Enabled by the high quality data from the Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope for the Galactic ASKAP HI (GASKAP-HI) survey, we investigate the potential magnetic alignment of the $\gtrsim 10\,{\rm pc}$-scale HI filaments in the Small Magellanic Cloud (SMC). Using the Rolling Hough Transform (RHT) technique that automatically identifies filamentary structures, combined with our newly devised ray-tracing algorithm that compares the HI and starlight polarisation data, we find that the HI filaments in the northeastern end of the SMC main body ("Bar" region) and the transition area between the main body and the tidal feature ("Wing" region) appear preferentially aligned with the magnetic field traced by starlight polarisation. Meanwhile, the remaining SMC volume lacks starlight polarisation data of sufficient quality to draw any conclusions. This suggests for the first time that filamentary HI structures can be magnetically aligned across a large spatial volume ($\gtrsim\,{\rm kpc}$) outside of the Milky Way. In addition, we generate maps of the preferred orientation of HI filaments throughout the entire SMC, revealing the highly complex gaseous structures of the galaxy likely shaped by a combination of the intrinsic internal gas dynamics, tidal interactions, and star formation feedback processes. These maps can further be compared with future measurements of the magnetic structures in other regions of the SMC.