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The field of gamma-ray astronomy opened a new window into the non-thermal universe that allows studying the acceleration sites of cosmic rays and the role of cosmic rays on evolutionary processes in galaxies. The detection of almost one hundred Galactic very-high-energy (VHE: 0.1−100TeV) gamma-ray sources in the Milky Way demonstrates that particle acceleration up to tens of TeV energies is a common phenomenon. Furthermore, the detection of VHE gamma rays from other galaxies has confirmed that cosmic rays are not exclusively accelerated in the Milky Way. The rapid development of gamma-ray astronomy in the past two decades has led to a transition from the detection and study of individual sources to source population studies. To answer the question, whether the VHE gamma-ray source population of the Milky Way is unique, observations of galaxies, for which individual sources can be resolved, are required. Such galaxies are the Magellanic Clouds, two satellite galaxies of the Milky Way, which have been surveyed by the H.E.S.S. experiment in the last decade. In this thesis, data from a total of 450 hours of H.E.S.S. observations towards the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC) are presented. During the analysis of the data sets, special emphasis is put on the evaluation of systematic uncertainties of the experiment in order to assure an unbiased flux estimation of the potential VHE gamma-ray sources of the Magellanic Clouds. A detailed analysis of the survey data revealed the detection of the gamma-ray binary LMCP3, the most powerful gamma-ray binary known so far, that is located in the LMC, and thus, increases the number of known VHE gamma-ray sources in the LMC to four. No other VHE gamma-ray source is detected in the Magellanic Clouds and integral flux upper limits are estimated. These flux upper limits are used to perform a source population study based on known VHE source classes and existing multi-wavelength catalogues. A comparison of the source populations of the Magellanic Clouds and the Milky Way revealed that no other source in the Magellanic Clouds is as bright as the most luminous VHE gamma-ray source in the LMC: the pulsar wind nebula N 157B, and that one-third of the source population of the Magellanic Clouds is less luminous than the other known VHE gamma-ray sources in the LMC. For only a couple of sources luminosity levels of Galactic VHE sources, that are more than one order of magnitude fainter than the detected sources in the LMC, are constrained. Based on the flux upper limits, differences on the TeV source populations in the Magellanic Clouds and the Milky Way as well as the importance of the source environments will be discussed.
Galaxy morphology is a fossil record of how galaxies formed and evolved and can be regarded as a function of the dynamical state of a galaxy. It encodes the physical processes that dominate its evolutionary history, and is strongly aligned with physical properties like stellar mass, star formation rate and local environment. At a distance of ∼50 and 60 kpc, the Magellanic Clouds represent the nearest interacting pair of dwarf irregular galaxies to the Milky Way, rendering them an important test bed for galaxy morphology in the context of galaxy interactions and the effect of the local environment in which they reside. The Large Magellanic Cloud is classified as the prototype for Magellanic Spiral galaxies, with one prominent spiral arm, an offset bar and an inclined rotating disc while the Small Magellanic Cloud is classified as a dwarf Irregular galaxy and is known for its unstructured shape and large depth across the line–of–sight. Resolved stellar populations are powerful probes of a wide range of astrophysical phenomena, the proximity of the Magellanic Clouds allows us to resolve their stellar populations to individual stars that share coherent chemical and age distributions. The coherent properties of resolved stellar populations enable us to analyse them as a function of position within the Magellanic Clouds, offering a picture of the growth of the galaxies’ substructures over time and yielding a comprehensive view of their morphology. Furthermore, investigating the kinematics of the Magellanic Clouds offers valuable insights into their dynamics and evolutionary history. By studying the motions and velocities of stars within these galaxies, we can trace their past interactions, with the Milky Way or with each other and unravel the complex interplay of forces that have influenced the Magellanic Clouds’ formation and evolution.
In Chapter 2, the VISTA survey of the Magellanic Clouds was employed to generate unprecedented high-resolution morphological maps of the Magellanic Clouds in the near-infrared. Utilising colour-magnitude diagrams and theoretical evolutionary models to segregate stellar populations, this approach enabled a comprehensive age tomography of the galaxies. It revealed previously uncharacterised features in their central regions at spatial resolutions of 0.13 kpc (Large Magellanic Cloud) and 0.16 kpc (Small Magellanic Cloud), the findings showcased the impact of tidal interactions on their inner regions. Notably, the study highlighted the enhanced coherent structures in the Large Magellanic Cloud, shedding light on the significant role of the recent Magellanic Clouds’ interaction 200 Myr ago in shaping many of the fine structures. The Small Magellanic Cloud revealed asymmetry in younger populations and irregularities in intermediate-age ones, pointing towards the influence of past tidal interactions.
In Chapter 3, an examination of the outskirts of the Magellanic Clouds led to the identification of new substructures through the use of near-infrared photometry from the VISTA Hemisphere Survey and multi-dimensional phase-space information from Gaia. The distances and proper motions of these substructures were investigated. This analysis revealed the impact of past Magellanic Clouds’ interactions and the influence of the Milky Way’s tidal field on the morphology and kinematics of the Magellanic Clouds. A bi-modal distance distribution was identified within the luminosity function of the red clump stars in the Small Magellanic Cloud, notably in its eastern regions, with the foreground substructure being attributed to the Magellanic Clouds’ interaction around 200 Myr ago. Furthermore, associations with the Counter Bridge and Old Bridge were uncovered through the detection of background and foreground structures in various regions of the SMC.
In chapter 4, a detailed kinematic analysis of the Small Magellanic Cloud was conducted using spectra from the European Southern Observatory Science Archive Facility. The study reveals distinct kinematics in the Wing and bar regions, attributed to interactions with the Large Magellanic Cloud and variations in star formation history. Notably, velocity disparities are observed in the bar’s young main sequence stars, aligning with specific star-forming episodes, and suggesting potential galactic stretching or tidal stripping, as corroborated by proper motion studies.