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[Gaia - Laboratoire LAGRANGE] ANR - GALHIS


Executive Summary:

This project aims at understanding the formation of the Milky Way from observations of the stellar populations which bear the imprint of early Galactic evolution in their chemical abundances, kinematics, and spatial distribution. We plan to study the inner regions of the Milky Way, where most of the stellar mass resides, in order to understand the physical process of formation of the bulge, either by early accretions, by gravitational collapse or by disc instability (bar or pseudo-bulge). Using our data sets, we will study the role of radial mixing in the evolution of the disc, the links and interaction between the bulge, the inner disc and the thick disc populations. We shall analyse about 30 fields distributed in the central regions and around, several millions of stars with photometry and astrometry (proper motions), several thousands stars with spectroscopy (elemental abundances and radial velocities), complemented by observations in the visible and near-infrared from public data. We shall analyse these data in several steps. First a detailed field by field analysis will allow to characterize the mean properties of each population. Second a global analysis of the various fields will be performed to understand the overall characteristics of the populations (mass distribution, mean metallicity, rotation and velocity ellipsoid, various spatial gradients) and the correlations between the parameters which are the tracers of the evolution (ages, chemical abundances, kinematics). We shall then be able to identify the characteristics which allow to distinguish different scenarios of formation of these populations (determination of the epoch of formation, history of star formation, identify tracers of merging events in different populations, role of the dynamical interaction between those populations, role of migrations). In parallel we shall integrate the results obtained from our analysis in a population synthesis model which will permit to ensure the consistency of parameters obtained with an overall scheme. This will also test the robustness of the results against possible bias and if necessary to find the method for correcting these bias. Gobal fitting of the model parameters (density laws, star formation rate, velocity ellipsoids, chemical and kinematical gradients, etc.) will also be performed using efficient model fitting method like the Monte Carlo Markov Chain approach in order to optimize the results and to deduce a global and consistent population model. We thus be able to test the most probable scenario explaining our observations. Dynamical tests will be done in order to ensure that the mass distribution deduced from the various observables is consistent with the kinematics observed. Two approaches will be used, one based on the Syer & Tremaine approach called "Made-to-Measure" which adapts the orbits of the Schwarzschild method to the observables, the other based on N-body and Tree SPH simulations from the approach of Semelin & Combes. Starting from initial conditions provided by LCDM scenarios it will simulate the (chemo-dynamical) evolution of a typical galaxy, of the same morphological type and mass as the Galaxy, which will be called by analogy a “ready-to-wear” model. Finally, we shalll be able to provide simulations in the form of mock catalogues, usable for the preparation of future projects, and in the framework of the Virtual Observatory. Our experience in large data



* Coordinator partner CASSIOPEE: 
- Hill Vanessa (Analysis and interpretation of the inner dic / bulge / bar relation. Stellar atmospheres, abundance analysis, spectroscopy.)
* Other members
- Recio- Blanco Alejandra (Thick disc observations and analysis, vertical structure of the disc. MATISSE stellar parameters algorithm.)
- De Laverny Patrick (Thick disc observations and analysis, co- ordinator of the global stellar atmospheres, abundance analysis.)
- Kordopatis Georges (Thick disc observations and analysis, vertical structure of the disc.)
- Ordenovic Christophe (Software developments for the MATISSE stellar parameters and chemical composition algorithm)

Other partners:
UTINAM (PI and coordinator: Annie Robin)
GEPI (partner coordinator: Misha Haywood)

 Duration: 36 months

The GALHIS project will support financially 1 post-odc per partner for 24 months.


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Monday 10 January 2011