Stellar history of the Small Magellanic Cloud in the era of deep photometric surveys
Creators: name: MASSANA ZAPATA, POL
Publisher: name: University of Surrey
Year: 2022

description: One of the key goals in modern astrophysics is to understand the origin of galaxies. Detailed studies of the various components of our Galaxy and its satellite galaxies allow us to reconstruct past events through present day clues. Essentially, we are unpicking the past history of our close systems on a galactic scale, carrying out what astronomers call "galactic archaeology''. The Milky Way (MW), its largest companion the Andromeda (M31) galaxy, and the smaller systems around them constitute the Local Group. Given their proximity, size, and interacting nature (among others), the largest satellites of our Galaxy, the Magellanic Clouds (MCs), provide optimum tests and constraints on galaxy formation and evolution theories as well as on the Lambda Cold Dark Matter (LCDM) paradigm. The aim of the present thesis is to further disentangle the formation and evolution of galaxies using the Small and the Large Magellanic Clouds (SMC/LMC) as laboratories. To achieve this, I present a careful study of the SMC stellar populations using the Survey of the MAgellanic Stellar History (SMASH), an unprecedentedly deep and wide survey of the MCs. I derive the SMC surface brightness profile in order to calculate the general parameters of the SMC, finding it very staggered. I trace the fainter outskirts by constructing a stellar density profile, uncovering a tidally disrupted stellar feature that reaches as far out as ~13 kpc from the SMC centre. I also serendipitously identify a faint feature of unknown origin located some ~15 kpc from the SMC centre that could be associated to a more distant structure. Comparing it observed tidal debris to in-house simulations of a 10^{9} solar masses SMC, I find that its elliptical shape can be explained by its tidal disruption under the combined presence of our Galaxy and the LMC. The SMC's older stellar populations present a smooth profile while its younger component has a jump in the density followed by a flat profile, confirming the heavily disrupted nature of this galaxy. I also present a quantitative study of the SMC resolved star formation history (SFH) and compare it with that of the LMC. I devise a strong link between the SFHs of the SMC and the LMC as far backwards in time as 3.5 Gyr ago, with three peaks of star formation at around 3, 2, 1.1 Gyr ago as well as a current enhancement. I test the robustness of these results against crowding issues and line-of-sight depth spread. The resulting resolved maps of star formation prove that the peak of star formation 2 Gyr ago had a much bigger impact across the SMC than in its larger companion. This peak is also the most conspicuous of them all, suggesting a very close encounter might have occurred with the LMC at around that time. Finally, I present a preliminary work on the three dimensional structure of the SMC using photometry of red clump stars alongside astrometric data from Gaia. The combination allows us to determine distances to every part of the galaxy. The hope is to be able to fully characterise the main tidal disruption of the galaxy.