Around the Sun, and up to ~3kpc from it, we have catalogued the structures in the Vr-Vphi plane of the Galactic disc, and we have been able to measure their gradients with distance. With this, we open the possibility to make an objective association between each of the substructures and a particular dynamical mechanism. For instance, resonances of the bar/spiral arms, or phase-mixing induced, probably, by the in-fall of the Sagittarius dwarf galaxy (Sgr).

Our search extends also to the very edge of the disc, where we have detected structures like the Monoceros ring. After almost 20 years since its discovery, it is still not clear whether it is the remnant of an accreted satellite, or the disc responding to the perturbation caused by the interaction with Sgr. Our results provide new observational constraints that can help us infer their origin.

Although Sgr can be related to many of the phase-space substructures of the disc, there are still many questions open regarding its orbit and stellar content, which hinders our ability to constrain its effects on the MW. I will also show how we have unveiled the almost 360º degrees continuous track of proper motions of the Sgr stream among the kinematic substructure of the MW halo thanks to smart use of the Gaia Archive. We have been able to isolate its stars and produced one of the largest samples of Sgr to date, composed of different stellar types. We have also produced the largest sample of RR Lyrae stars and used photometric distances and proper motions to characterize the stream in 5D (positions+tangential velocities) as well as to study in detail features like the bifurcation. The proper motion tracks of these samples show some differences with existing models of the stream, which opens the possibility to improve our current understanding of its in-fall history.

The challenge now is to unravel the connection between the different components of the MW and obtain a gravitational potential that can account for all of the phase-space structures catalogued in this thesis.

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The public defence will take place online, through videoconferencing with Microsoft Teams. Those who are interested in attending have to request access to the virtual meeting room by sending an email to the president of the Comissió de Doctorat de la Facultat de Física (Dr. Eugeni Graugés Pous - vd.fisica.recerca@ub.edu).

President: Dr. Alice C. Quillen

Secretary: Dr. Mark Gieles

Vocal: Dr. Jorge Peñarrubia