Dark matter is one of the biggest mysteries of the Universe. Its properties cannot be explained with the known laws of physics and elementary particles. Yet, it is the most abundant form of matter... Show moreDark matter is one of the biggest mysteries of the Universe. Its properties cannot be explained with the known laws of physics and elementary particles. Yet, it is the most abundant form of matter in the Universe.Several dark-matter theories exist, including cold dark matter (CDM), self-interacting dark matter (SIDM), and fuzzy dark matter (FDM). These theories make different predictions for the density profiles of dark-matter haloes (cuspy or cored), depending on the nature (CDM, SIDM, FDM) and properties (self-interaction strength, FDM particle mass) of dark matter. These profiles can be determined from the stellar kinematics of the galaxies hosted by the haloes. Many massive dwarf galaxies show cored profiles. However, baryonic processes such as star formation may also induce cores.In this thesis, I test CDM, SIDM, and FDM using the faintest and most dark matter–dominated galaxies, ultra-faint dwarf galaxies (UFDs), which offer a new perspective on the cusp–core problem. The stellar kinematics of UFDs should not be significantly affected by baryonic processes. I find that UFDs have no detectable cores, implying that the cores of more massive dwarf galaxies are not caused by dark-matter physics. I can also exclude the previously promising particle masses ~10^-22 eV/c^2 for FDM. Show less
One of the most important puzzles in modern astrophysics is the nature of dark matter. Stellar streams, formed by tidal stripping of the stars from globular clusters or dwarf galaxies, behave as a... Show moreOne of the most important puzzles in modern astrophysics is the nature of dark matter. Stellar streams, formed by tidal stripping of the stars from globular clusters or dwarf galaxies, behave as a group of test particles allowing us to measure the Milky Way’s dark matter content and, therefore, offering us a key to understanding its nature. Open clusters, loosely bound groups of stars that move through the Galaxy together, are, in contrast, an important driver of stellar evolution research. This Thesis presents our studies of these Galactic substructures and the conclusions we can draw on the larger Universe and physics based on these local observations. In chapters 2 - 4, we apply a novel method to map the Milky Way’s dark matter content using stellar streams, taking care to understand the various possible contributors to the systematics. Chapter 5 is dedicated to the study of the Hyades open cluster. Show less
This is an erratum to the paper ‘Galactic potential constraints from clustering in action space of combined stellar stream data’ (Reino et al. 2021). In the original paper, there were errors in our... Show moreThis is an erratum to the paper ‘Galactic potential constraints from clustering in action space of combined stellar stream data’ (Reino et al. 2021). In the original paper, there were errors in our action-space probability density estimates when considering multiple streams in combination. The errors do not stem from our overall procedure but from a technical limitation of our density estimator, that was not known to us, or the author of the density estimator, a priori. Show less
