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Abstract

Dwarf galaxies in the Milky Way (MW) system provide us with important information of the star formation in the early Universe. In particular, extremely metal-poor stars in them are likely to form in the environment that is directly influenced by the first stars. In this thesis, I utilise the semi-analytic code a-sloth to study the properties of these dwarf galaxies. A new star formation model that allows tracking of individual stars is implemented. The star formation efficiency is important in determining the stellar mass of ultra-faint galaxies at z = 0. To better quantify the goodness-of-fit of the physical models, I develop a new analysis method, which utilises the unsupervised clustering. With this method, the results suggest that the fiducial model cannot reproduce the mean metallicity of the dwarf galaxies. A temporary improvement of the model is implemented and the goodness-of-fit improves by a factor of 2, compared to the fiducial model. I further analyse the location of EMP stars of MW/M31-like systems in the hydrodynamical simulation TNG50. The analysis is based on the spatial and kinematic information of stars. I find that EMP stars reside mostly in the Stellar halo in the galaxy, regardless of the definition of EMP stars. The model and analysis methods introduced in this thesis provide a new framework for future works to understand dwarf galaxy formation and stars that reside in them.