A Detailed GASKAP-HI View of Shells and Loops in the Magellanic Bridge

Abstract

We present 8 pc-scale GASKAP-H i observations of an H i shell (diameter ~130 pc) associated with the Hα shell DEM171 in the Magellanic Bridge. The Bridge’s diffuse, H i-dominated environment, with minimal galactic shearing and fewer overlapping star-forming regions, provides an ideal environment to study cold gas formation driven by stellar feedback. To investigate the H i multi-phase structure and kinematics of the shell, we perform Gaussian decomposition of H i line profiles. We identify cold H i components with velocity dispersions σ < 2.5 km s−1 located within the shell. Complementary Herschel far-infrared (FIR) 250$\rm{$\umu $m}$ and Hα maps show that while the central cavity is ionized, the shell walls contain cold H i, molecular gas, and dust, suggesting that stellar feedback has promoted cold gas formation or swept pre-existing cold gas into the shell walls. We also identify cold H i clumps outside the shell tracing a larger-scale structure, MB-Loop I. To investigate the large-scale context, we apply a Fourier transform method to H i emission-line profiles to map the lower limit of cold-gas column densities across a section of the Bridge, revealing structures from large loops to smaller shells. The association between MB-Loop I and the H i shell suggests that cold H i gas may pre-exist before shell expansion. Finally, the shell exhibits asymmetric expansion, with a preferred orientation roughly perpendicular to the arc along MB-Loop I. Our results show that cold H i gas exists across a wide range of spatial scales in the Magellanic Bridge, highlighting the dynamic interplay that shapes the surrounding interstellar medium.