The densest stellar systems in the Universe: The nuclear stellar disc
Författare
Summary, in English
Understanding the formation and evolution of galaxies and in particular their galactic centres is one of the most intriguing questions in modern astrophysics. Many spiral galaxies like the Milky Way feature a nuclear stellar disc (NSD) in their centre. The Milky Way's NSD is, together with the nuclear star cluster and the central super massive black hole, one of the main inner components and best local laboratories available for studying galaxy evolution. Because of high extinction, crowding, and the superposition of multiple structures along the line of sight, studies of the inner regions of the Milky Way are however very challenging and very little has been done so far. Thanks to recent data, this thesis aims at unveiling the physical processes which led to the formation of the NSD and its links with the other components of the Milky Way. This manuscript is divided into three parts corresponding to the different methodologies used.
For the first part, thanks to high-resolution near-infrared spectroscopy, I carried out a chemical analysis of cool giant stars located in the inner Galactic bulge. I measured detailed abundances of the alpha-elements: silicon, magnesium and calcium, using recent and precise theoretical data such as an updated line list, broadening parameters and non-local thermodynamic equilibrium corrections. Based on the derived abundances, a tailored chemical evolution model for the inner Galactic bulge was constructed. I also used spectral analysis to measure the carbon isotopic ratio automatically in solar neighbourhood giant stars in order to establish a relation with asteroseismic stellar mass. This would allow to estimate stellar ages in distant regions such as the NSD.
In the second part of this thesis, I studied the dynamics of stars observed in the Milky Way's NSD by doing an orbital analysis. I computed orbits in a non-axisymmetric gravitational potential accounting for the effects of the Galactic bar and derived their fundamental frequencies. This allowed me to identify the orbital resonances and then the different orbit families that may be present in the NSD.
In addition to observations, simulations are of great interest to fully understand the physical processes that formed the inner regions of the Galaxy. In this final part, I used a N-body hydrodynamic simulation of an isolated Milky Way like galaxy in order to study the formation of its NSD. This simulation allowed to do a first comparison between observations and simulations in terms of chemistry and dynamics.
For the first part, thanks to high-resolution near-infrared spectroscopy, I carried out a chemical analysis of cool giant stars located in the inner Galactic bulge. I measured detailed abundances of the alpha-elements: silicon, magnesium and calcium, using recent and precise theoretical data such as an updated line list, broadening parameters and non-local thermodynamic equilibrium corrections. Based on the derived abundances, a tailored chemical evolution model for the inner Galactic bulge was constructed. I also used spectral analysis to measure the carbon isotopic ratio automatically in solar neighbourhood giant stars in order to establish a relation with asteroseismic stellar mass. This would allow to estimate stellar ages in distant regions such as the NSD.
In the second part of this thesis, I studied the dynamics of stars observed in the Milky Way's NSD by doing an orbital analysis. I computed orbits in a non-axisymmetric gravitational potential accounting for the effects of the Galactic bar and derived their fundamental frequencies. This allowed me to identify the orbital resonances and then the different orbit families that may be present in the NSD.
In addition to observations, simulations are of great interest to fully understand the physical processes that formed the inner regions of the Galaxy. In this final part, I used a N-body hydrodynamic simulation of an isolated Milky Way like galaxy in order to study the formation of its NSD. This simulation allowed to do a first comparison between observations and simulations in terms of chemistry and dynamics.
Avdelning/ar
Publiceringsår
2024
Språk
Engelska
Dokumenttyp
Doktorsavhandling
Förlag
Lund University
Ämne
- Astronomy, Astrophysics and Cosmology
Nyckelord
- stars : abundances
- stars: late-type
- Galaxy: dynamics
- Galaxy: centre
- Galaxy: structure
Aktiv
Published
Handledare
- Nils Ryde
- Mathias Schultheis
ISBN/ISSN/Övrigt
- ISBN: 978-91-8104-165-1
Försvarsdatum
27 september 2024
Försvarstid
09:00
Försvarsplats
Observatoire de la Cote d'Azur, France
Opponent
- Patricia Sánchez-Blázquez (Profesor Titular)