Abstract
The Milky Way, our home galaxy, is a cornerstone for understanding galaxy formation. The Galaxy is shaped through mergers and star formation, and its stars preserve invaluable chemical and dynamical clues about its assembly. This thesis uses metal-poor stars--relics of the earliest epochs--to map the Galactic halo and trace the ancient Galaxy.
Part I investigates the inner and outer halo: Chapter 2 maps the inner halo using Gaia DR3 proper motion and photometry and identifies density variations in stellar streams like GD-1 and Jhelum. Chapter 3 shows that very metal-poor (VMP) stars ([Fe/H] < -2) are 60 times rarer than metal-poor stars ([Fe/H] < -1) in the inner halo, offering additional insights into its metallicity distribution function (MDF). Chapter 4 maps the outer halo using metal-poor giant stars, inferring its MDF and revealing substructures, including the VMP stellar counterpart to the Magellanic Stream.
Part II focuses on the Milky Way’s earliest stages: Chapter 5 reanalyses Gaia RVS spectra, identifying a new sample of 1000 bright VMP stars suitable for high-resolution spectroscopic follow-up. Chapter 6 uses the spectroscopic follow-up of Pristine-Gaia photometric metallicities (with a 77% success rate in finding [Fe/H] < -2.5 stars), mapping new members of the most metal-poor C-19 stream and the excess of VMP stars in disc-like orbits. Chapter 7 models the turbulent proto-Galaxy's rotational coherence using Gaia data, showing a slow, monotonic transition to an ordered, rotating old disc.
Overall, this thesis underscores the power of metal-poor stars in studying the ancient Milky Way.
Part I investigates the inner and outer halo: Chapter 2 maps the inner halo using Gaia DR3 proper motion and photometry and identifies density variations in stellar streams like GD-1 and Jhelum. Chapter 3 shows that very metal-poor (VMP) stars ([Fe/H] < -2) are 60 times rarer than metal-poor stars ([Fe/H] < -1) in the inner halo, offering additional insights into its metallicity distribution function (MDF). Chapter 4 maps the outer halo using metal-poor giant stars, inferring its MDF and revealing substructures, including the VMP stellar counterpart to the Magellanic Stream.
Part II focuses on the Milky Way’s earliest stages: Chapter 5 reanalyses Gaia RVS spectra, identifying a new sample of 1000 bright VMP stars suitable for high-resolution spectroscopic follow-up. Chapter 6 uses the spectroscopic follow-up of Pristine-Gaia photometric metallicities (with a 77% success rate in finding [Fe/H] < -2.5 stars), mapping new members of the most metal-poor C-19 stream and the excess of VMP stars in disc-like orbits. Chapter 7 models the turbulent proto-Galaxy's rotational coherence using Gaia data, showing a slow, monotonic transition to an ordered, rotating old disc.
Overall, this thesis underscores the power of metal-poor stars in studying the ancient Milky Way.
| Original language | English |
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| Qualification | Doctor of Philosophy |
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| Award date | 6-Dec-2024 |
| Place of Publication | [Groningen] |
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| Print ISBNs | 978-94-6496-287-1 |
| DOIs | |
| Publication status | Published - 2024 |