GEPI

Disk galaxies present a great regularity in their stellar bodies but reveal complex structures in their young stars and gas. What connects the highly structured birth conditions to the overall regularity of disk galaxies ? To tackle this question, we can use the Milky Way, for which we have star-by-star data, as a model organism and study the processes that dominated the evolution of its disk. The recent technical advances in spectroscopic and astrometric surveys have made possible to collect 6D phase-space information, abundances and ages for a large number of individual stars. I will present a statistical model for the evolution of the Milky Way disk ; the model describes when and where its stars were born, with what metallicity, and how their orbit subsequently evolved until their present state. APOGEE red clump stars and Gaia constrain that model well, with an inside-out growth consistent with redshift-size evolution of other galaxies, sensible enrichment and extensive radial migration : over the age of the low-alpha disk, the typical migration distance is about the disks half-mass radius. This extensive radial migration appears to happen with only modest radial orbit heating. Consequently, the disk looks very regular without loosing its radial gradients.