This project aims at constraining our knowledge of our Galaxy formation and evolution using the coming second data release of the Gaia mission.
The availability of the Gaia data gives the opportunity to improve our understanding of the physical processes on-going in galaxy formation and evolution. Gaia provides complete samples with an accuracy never reached before on parallaxes and proper motions, 6D space informations for million of stars. Gaia data are also very well complementary with ground based spectroscopic surveys such as APOGEE, Gaia-ESO and forthcoming WEAVE surveys.

In the last 30 years, we have developed a method to interpret complex data sets for Galaxy evolution studies, based on the population synthesis approach. The Besançon Galaxy Model (BGM) incorporates a scenario for the formation and evolution of the Milky Way and translate it into simulations of observations, taking into account selection effects and observational errors. This approach allows to confront our understanding of the physics of Galaxy evolution in detail, including various aspects, dynamics, stellar evolution, interstellar matter distribution, with real data through simulations. Changing the scenario and the underlying hypotheses, and confronting the resulting simulations with real survey data, will allow us to constrain our knowledge about galactic evolution, and to reach a global self-consistent view of the installation of the Galaxy components along the evolution of the Milky Way, including non-stellar components, such as interstellar matter and dark matter.

With the help of ISSI, we aim at combining our expertises in the development of this approach in the analysis of Gaia data. Meetings in Bern will help us to discuss in details and to exploit Gaia data to

1) Compare model simulations, testing several hypothesis, with Gaia data, allowing to detect possible inconsistencies, and correcting hypothesis via Monte Carlo Markov Chain methods;

2) obtain a comprehensive view of the Galactic plane sub-structures, in particular the bar, spiral arms, warp and flare, taking into account the dynamics;

3) set constraints on stellar physics by confronting the star models used in the population synthesis with luminosities measured by Gaia, complemented by spectroscopy and asteroseismology;

4) provide efficient tools to compute orbits for stars observed with Gaia, and make these tools available on line for the community.

This ambitious project brings in the experiences of an international team with complementary expertises in populations synthesis modelling (Besançon, Barcelona), galactic dynamics (Strasbourg, Barcelona, Conception, Chile), interstellar matter studies (Saclay, Besançon), data analysis and data mining (Barcelona), microlensing (Manchester, UK) that will allow to conduct the project for the benefit of the astronomical community.