On the dynamics of the Small Magellanic Cloud through high-resolution ASKAP HI observations

We use new high-resolution HI data from the Australian Square Kilometre Array Pathfinder to investigate the dynamics of the Small Magellanic Cloud (SMC). We model the HI gas component as a rotating disc of non-negligible angular size, moving into the plane of the sky, and undergoing nutation/precession motions. We derive a high-resolution (similar to 10 pc) rotation curve of the SMC out to R similar to 4 kpc. After correcting for asymmetric drift, the circular velocity slowly rises to a maximum value of V-c similar or equal to 55 km s(-1) at R similar or equal to 2.8 kpc and possibly flattens outwards. In spite of the SMC undergoing strong gravitational interactions with its neighbours, its HI rotation curve is akin to that of many isolated gas-rich dwarf galaxies. We decompose the rotation curve and explore different dynamical models to deal with the unknown 3D shape of the mass components (gas, stars, and dark matter). We find that, for reasonable mass-to-light ratios, a dominant dark matter halo with mass M-DM(R < 4 kpc) similar or equal to 1-1.5 x 10(9)M(circle dot) is always required to successfully reproduce the observed rotation curve, implying a large baryon fraction of 30 per cent-40 per cent. We discuss the impact of our assumptions and the limitations of deriving the SMC kinematics and dynamics from HI observations.