Substructure in the phase-space of the Galaxy with Gaia
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 Mil...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2020 |
| País: | España |
| Institución: | CBUC, CESCA |
| Repositorio: | TDR. Tesis Doctorales en Red |
| OAI Identifier: | oai:www.tdx.cat:10803/670916 |
| Acceso en línea: | http://hdl.handle.net/10803/670916 |
| Access Level: | acceso abierto |
| Palabra clave: | Dinàmica estel·lar Dinámica estelar Stellar dynamics Via Làctia Vía Láctea Milky Way Ciències Experimentals i Matemàtiques 52 |
| Sumario: | 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. |
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