Gaia: new perspectives in understanding the galacticbulge

Abstract

Although the Milky Way bulge is our closest opportunity to study in detail such a complexchemo-dynamical system, its formation and evolution is still poorly understood. The highextinction, the crowding, and the superposition of multiple structures along the line ofsight make studies of the inner Galactic regions challenging. Two main scenarios have beeninvoked for the bulge formation: gravitational collapse or hierarchical merging ofsubclumps and secular evolution of the disc through a bar forming a pseudo-bulge. Recentresults suggest that the Galactic bulge could be the result of both formation processes.Gaia will be limited by the extinction and the crowding but will still observe accuratelymore than 20 million bulge stars (Robin et al. 2005). The Gaia parallaxes and proper motions will probe the structureof the Galactic inner regions, will allow to obtain a clean bulge sample and will solvethe different biases in distance currently present in the bulge surveys. Radial velocitieswill also be obtained for the brightest stars in the less crowded regions, providing 6Dconstrains to dynamical models. Completed by ground-based abundances, the Gaia bulgesurvey will provide unique constraints on the formation history of the Galactic innerregions.