"Off piste" beyond the disc of the Milky Way: Structure of the stellar halo and dynamics of nearby dwarf galaxies

In this thesis we have exploited state-of-the-art datasets and techniques and/or proposed new methods to study the matter distribution in the stellar halo of our Galaxy and to study the kinematics and dynamics properties of a sample of nearby dwarf irregular galaxies (dIrrs). In the first part of the thesis, we focused on the study on the stellar halo of the Milky Way. In particular, we exploited the first data release of Gaia obtaining the first all-sky view of the RR Lyrae distribution in the inner part of the stellar halo. In the second part of this thesis, we studied the HI kinematics of 17 nearby dIrrs extracted from the LITTLE THINGS survey. Concerning the analysis of HI datacubes, our approach differs significantly from previous studies in that we exploit the 3D dimensions (two spatial dimensions and one spectral dimension) of the data using a state-of-the-art 3D fitting tool. In the last part of the thesis, we exploited the results obtained in the analysis of the dIrrs focusing on two important scaling relations: the “baryonic Tully-Fisher relation” and the “radial acceleration relation”. We compared our results with the ones obtained in previous works focusing on more massive galaxies. Finally, we made use of the velocity dispersions and of the star formation rates of the dIrrs in our sample to investigate whether the observed turbulence in the HI can be sustained by the energy injected in the ISM by the star formation activity.