The Small Magellanic Cloud: showing the scars of a survivor of galactic cannibalism

The Large and Small Magellanic Clouds (LMC/SMC) provide excellent laboratories for understanding how galaxies form and evolve. Due to their close proximity, we can study their stellar populations in exquisite detail. The goal of this thesis is to determine the structure and dynamical state of the smallest system, the SMC. To achieve this, I present new spectroscopic data for ̴3000 SMC Red Giant Branch (RGB) stars observed using the AAOmega spectrograph at the Anglo-Australian Telescope. I complement the data with further spectroscopic measurements from previous studies that used the same instrumental configuration as well as with proper motions from the Gaia Data Release 2 and Early Data Release 3 catalogues. Analysing the stellar kinematic data, I find that the SMC centre of mass presents a conspicuous offset from the velocity centre of its associated neutral hydrogen H I gas, suggesting that the SMC gas is likely to be far from dynamical equilibrium. Furthermore, I find evidence that the SMC is currently undergoing tidal disruption by the LMC within 2 kpc of the centre of the SMC, and possibly all the way into the very core. This is revealed by a net outward motion of stars from the SMC centre along the direction towards the LMC and an apparent tangential anisotropy at all radii. The latter is expected if the SMC is undergoing significant tidal stripping, as we demonstrate using a suite of N-body simulations of the SMC/LMC system disrupting around the Milky Way. To shed light on the above I built a mass model of the SMC by using the Binulator+GravSphere Jeans modeling tool. I assume the SMC to be made up by a bound core surrounded by an extended field of tidal debris and, by allowing the model to discard the information carried by the debris, I derive both the density and the anisotropy profile of the SMC. I use the density profile recovered by the model to probe the Dark Matter distribution of the SMC. I also used the spectroscopic data to derive metallicities for the RGB population and serendipitously found the possible traces of a small, extremely metal poor object within the SMC