Abstract
In the current cosmological model, the Lamda Cold Dark Matter model (ΛCDM), dark matter is thought to make up the vast majority (∼ 85%) of the matter in the Universe, and it forms the backbone of structure formation. Yet, due to the elusive properties of dark matter, we still know very little about it. The particle nature of dark matter is one of the most pressing, unanswered questions in astrophysics.
Despite the considerable success of the ΛCDM model at explaining large-scale structure formation in the Universe, there are a number of outstanding tensions between the model and observations at small (dwarf galaxy) scales. Understanding these tensions is key to our understanding of dark matter, making dwarf galaxies ideal probes. Fortunately, within the observable region that we reside in, known as the Local Group, there is an abundance of dwarf galaxies covering a broad range of properties. In this thesis, I primarily focus on investigating the dark matter content of the dwarf galaxy satellites of our galactic neighbour, the Andromeda galaxy (M31).
First, I present results from the dynamical mass modelling analysis of Andromeda (And) XXV. Intriguingly, I find And XXV has an unusually low central dark matter density when compared to other dwarfs of a similar mass. In a follow-up study, I then investigate possible causes of the low central densities observed in both And XXV and And XXI (identified to have a similarly low central density in a previous study). I test the effects of stellar feedback, tidal stripping and halo concentrations, as well as a range of different dark matter models. I find that in both cold and warm dark matter, stellar feedback alone cannot explain the densities. Instead, And XXV requires a combination of stellar feedback and extreme tidal stripping, whereas And XXI favours stellar feedback and an extremely low halo concentration. Finally, I detail the discovery of two ultra-faint dwarf galaxies around M31 and Triangulum (M33). Both of these dwarfs have tantalising features, which could have potential ramifications for our understanding of dwarf galaxy evolution.
The work I present in this thesis lays the groundwork for analysing the remaining M31 dwarf galaxies. When combined with the upcoming mass modelling of the entire M31 system, as well as the wealth of dwarfs posited to be discovered by upcoming astronomical surveys, the methods presented in this thesis will provide robust constraints on both the nature of dark matter and galaxy formation and evolution pathways.