Galactic research has entered a thrilling epoch.

Our knowledge of Galactic stellar populations, until few years ago mostly confined to stars at the solar vicinity, is rapidly extending to large regions of the disc and bulge of our Galaxy. Large spectroscopic surveys (GES, APOGEE, GALAH, ..) are acquiring an unprecedented amount of data, with radial velocities and chemical composition for hundred thousands stars, from the innermost regions to the periphery of the Milky Way disc. This unique, because unprecedented, cartography of our Galaxy will acquire all its potential with the publication of the data from Gaia, the European astrometric mission, which will deliver positions and proper motions for 1 billion objects, and radial velocities for about one tenth of them. Without waiting for the final catalogue of the mission (planned for ~ 2022), by early 2017, the astrometric solution for most the sky will be made public, together with radial velocities for some ten millions stars. In less than two years from now, we will thus be able to reconstruct the orbits of several millions stars in the Galaxy, to have detailed chemical abundances for some hundred thousands and ages for several thousands.

The tremendous amount of data that the Gaia mission will deliver, together with those of  spectroscopic missions already available, constitutes an exceptional testbed for all numerical models aiming at quantifying the evolution of MW-type galaxies as a function of redshift. The Milky Way now offers the unique opportunity to test models predictions, constrain the efficiency of different processes as a function of time, and ultimately help in decoding the puzzle of the evolution of disc galaxies. As examples, the transition from an initial, violent phase of evolution of our Galaxy to a more quiescent, secular one is probably encoded in the Galactic thick and thin disc stellar populations, respectively:  from chemistry-age relations, it is possible to derive information about the star formation efficiency and related feedback at early epochs, from their dispersions it starts to be possible to constrain the steepness of metallicity gradients at high redshift, their evolution with redshift and the amount of gas accretion that the Galaxy experienced over time. Secular evolutionary processes, like bar formation and evolution, radial migration, etc leave specific signatures that can be tested on current data, where traces of past satellites accretion events are also found.

The aim of this two-days workshop is thus to bring together modelers and observers working on different fields (Galactic stellar populations and dynamics, high redshift universe, ISM physics, ..) to make the point on the most recent discoveries about the Galaxy and the challenges they present for all models of galaxy evolution.

This workshop aims to build bridges with a broader audience than that specifically working on Gaia. For this, we warmly invite researchers working on extragalactic topics to join our meeting, to start a common discussion on how the Milky Way fits in the current scheme of formation and evolution of disc galaxies, and the challenges that our Galaxy presents for interpreting extragalactic discoveries.

This workshop is organized by the AS Gaia, with the support of the PNCG, in Nice on December 17 and 18.

It will follow «Les Journées PNCG » organized in Nice on the 15 and 16th December.

People interested in participating can send an email to mod.gaia@obspm.fr

before November 15, 2015.

The organizers,

M. Haywood, V. Hill, P. Di Matteo