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Archéologie galactique : contraintes observationnelles aux modèles de formation du disque épais

Abstract : In the era of large spectroscopic surveys, galactic archaeology aims to disentangle the merging history of the Milky Way by finding relics of past accretion events. The goal of this thesis is to shed light to the understanding of the formation of the galactic thick disc by analysing 700 low resolution spectra obtained in the near infrared. The tools and the methods that are developed in this work will have a direct applicability to the spectral parameterisation of the Gaia data, which will collect spectra in roughly the same configuration. Two algorithms have been investigated, MATISSE and DEGAS, and a hybrid approach combining these two methods has been proposed in order to derive the stellar atmospheric parameters (effective temperature, surface gravity, overall metallicity). In addition, we have implemented tools in order to obtain the galactocentric distances of the targets, based on stellar isochrones. Once applied on our data sample, full spatial and kinematic coordinates have been obtained. This allowed us to assign the targets to one of the main galactic components, i.e. the thin disc, the thick disc or the halo. We found that the properties of the thick disc outside the solar neighbourhood differ only slightly from the thick disc properties as derived in the solar vicinity. Without ruling out in a definitive way the existence of intrinsic vertical gradients in the thick disc, it has been shown that the vertical trends that we measured can be explained as a smooth transition between the different galactic components. In addition, a correlation between the orbital rotational velocity and the metallicity has been detected. This gradient challenges formation scenarios of the thick disc based on a radial migration of the stars from the inner regions of the Galaxy. Finally, estimations of the scale height and the scale length for different metallicity bins of the thick disc result in consistent values, showing no evidence of relics of destroyed massive satellites. The combination of the kinematical and chemical information that has been obtained in this work, favours formation scenarios based either on a gas rich satellite merger, or the dynamical heating of a pre-existent thin disc by minor mergers.
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https://tel.archives-ouvertes.fr/tel-00736775
Contributor : Kordopatis Georges <>
Submitted on : Monday, October 1, 2012 - 11:57:36 AM
Last modification on : Wednesday, October 14, 2020 - 4:22:26 AM
Long-term archiving on: : Friday, December 16, 2016 - 6:51:47 PM

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  • HAL Id : tel-00736775, version 1

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Georges Kordopatis. Archéologie galactique : contraintes observationnelles aux modèles de formation du disque épais. Astrophysique galactique [astro-ph.GA]. Observatoire de Paris, 2011. Français. ⟨tel-00736775⟩

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