A Galactic Transformation—Understanding the SMC’s Structural and Kinematic Disequilibrium
Abstract
Abstract The SMC is in disequilibrium. Gas line-of-sight (LOS) velocity maps show a gradient of 60–100 km s −1 , generally interpreted as a rotating gas disk consistent with the Tully–Fisher relation. Yet, the stars don’t show rotation. Despite a small on-sky extent (∼4 kpc), the SMC exhibits a large (∼10 kpc) LOS depth, and the stellar photometric center is offset from the HI kinematic center by ∼1 kpc. With N -body hydrodynamical simulations, we show that a recent (∼100 Myr ago) SMC–LMC collision (impact parameter ∼2 kpc) explains the observed SMC’s internal structure and kinematics. The simulated SMC is initialized with rotating stellar and gaseous disks. Post-collision, the SMC’s tidal tail accounts for the large LOS depth. The SMC’s stellar kinematics become dispersion dominated ( v / σ ≈ 0.2), with radially outward motions at R > 2 kpc, and a small (
Fields of Study & Subjects
Astrophysics and Star Formation Studies
Stellar
planetary
and galactic studies
Astronomy and Astrophysical Research
Publication details
- Journal / source
- The Astrophysical Journal
- Publisher
- American Astronomical Society
- Volume
- 1000
- Issue
- 1
- Pages
- 50–50
- Publication date
- 16 March 2026
- Language
- EN