[ca] Des del moment en que la Via Làctia (VL) va néixer, diferents mecanismes dinàmics han anat interactuant i modificant la distribució d'estels a l'espai de fases. Aquesta tesi està enfocada a la detecció i caracterització de la subestructura cinemàtica present a les dades del satèl·lit Gaia, en diferents projeccions de l'espai de fases. De l'estudi del pla de velocitats Vr-Vphi hem obtingut la llista més completa de grups mòbils (grups d'estrelles amb cinemàtica coherent), amb la que hem estudiat com la seva localització dins del pla varia en funció d'on estiguem de la Galaxia. Els gradients en funció del radi i azimuth Galactocèntrics que hem mesurat ens han permès, per primer cop, fer una associació temptativa de cada estructura amb un mecanisme dinàmic diferent: ressonàncies amb la barra/braços espirals o phase-mixing, probablement induït per la interacció amb la galaxia nana de Sagitari (Sgr). En estudiar les parts llunyanes del disc, hem detectat les estructures de Monoceros i ACS a partir solament de la seva cinemàtica, a diferència dels estudis anteriors. Aquestes estructures, que gràcies als nostres resultats s'han pogut veure de forma més clara que mai, estan probablement causades també per Sgr i, amb les dades que aportem, ara serà possible testejar de forma acurada aquesta hipòtesi (contrastant-la amb d'altres que existeixen a la literatura). Finalment, aquesta mateixa metodologia ens ha permès també identificar la signatura cinemàtica del corrent estelar de Sgr de forma empírica i homogènia en tot el cel. La mostra resultant és la més gran existent actualment i aporta les dues components de la velocitat que fins ara havien faltat: moviments propis al llarg de tota la estructura. D'altra banda, aplicant un metodologia diferent, hem compilat la mostra més gran de RR Lyrae pertanyents al corrent de Sgr. Per aquestes estrelles es poden obtenir distàncies molt precises i, combinades a l'altre mostra de Sgr, permetran modelar de forma detallada l'òrbita passada d'aquesta galàxia nana. La combinació de tots els nostres resultats connecta la cinemàtica del disc amb la de l'halo i obra la porta a caracteritzar, per primer cop, la història de la VL de forma híbrida.

[en] The Gaia mission and its extensive catalogue of stars has marked the beginning of the Golden Age of Galactic dynamics. We have now access to the kinematics of more than a billion stars with which we can start deciphering the history of our Galaxy. Before Gaia, we knew that the phase-space of the Milky Way (MW) contained a wealth of substructure created by the different dynamical processes and components of the Galaxy, but we did not have enough kinematical data with which to characterise it with precision outside the Solar neighbourhood (SN). In this thesis we set out to detect and describe the kinematic substructure of the MW, not only near the Sun but to the very limit of the Gaia sphere. Our goal is to characterise the phase-space features of our Galaxy, introducing novel empirical measurements that can help us understand the structure of the MW and its evolution, together with the dynamics of its different components (bar, spiral arms, halo, satellites), and the interactions among them over time. We will focus on the disc and the structures of the halo, in particular, the Sagittarius (Sgr) dwarf spheroidal, a galaxy undergoing full tidal disruption and most likely a significant perturber in the recent history of our Galaxy. Our methodology is centred on the analysis of the Gaia DR2 data mostly using the wavelet transformation (WT) that is a robust statistical tool to reveal the substructure present in the velocity maps. We apply it on the plane of Galactocentric radial velocity (vR) against rotational velocity (vφ), venturing into regions beyond the SN, but also, and for the first time, to the proper motion histograms of distant stars all around the sky. As a result, we find that the velocity field of the MW disc is highly structured not only at the SN but, at least, up to distances of ∼3kpc. We have characterised the shape of each structure and described their changes with position in the Galaxy. We report that the vφ of each structure decreases with Galactocentric radius in a different way, which allows us to associate tentatively each structure with a different dynamical mechanism, namely, the phase-mixing process most likely initiated by the last pericentre passage of Sgr, and the resonances with the non-axisymmetric components of the MW (bar and/or spiral arms). Additionally, we detect two arch-like structures towards the anticentre corresponding to Monoceros and Anticentre stream (ACS). Thanks to our method, we are able to observe their morphology sharper than ever and produce a kinematic selection of member stars. From this, we obtain a precise characterisation of Monoceros and ACS that can be now used to compare quantitatively the models proposed to explain their origin. Based on our preliminary analysis, we favour the scenario in which they were caused by the repeated perturbations induced by Sgr, as opposed to being disrupted satellites as some authors propose. With respect to Sgr, we have detected the kinematic signature of its stream across the whole sky, and measured the proper motion of this system along a large portion of the tidal tails, which was not possible before Gaia. We have shown also that the predictions of the models do not match our observations, and thus require revision. The resulting sample of candidate stars represents a vast catalogue of stars of different stellar types that can be used to model the orbit of Sgr, as well as their distribution along the stream and its link to the star formation history. Finally, we complement this sample with the largest list of RR Lyrae in Sgr. In doing so, we have obtained a precise characterisation of the 3D distribution of its tidal debris as well as its tangential velocities, mostly unexplored until now as these require distances and proper motions simultaneously. All together, we have provided a detailed characterisation of the kinematic substructure present throughout the MW that we can now use to study and model the evolution of our Galaxy and its components in a global, transverse manner which takes into account the coupling between the Sgr stream and the disc.