André Martins (Besançon Observatory – Institut UTINAM): Constraining the Milky Way formation and evolution with MCMC/ABC method

The Besançon galaxy model (Robin et al. 2003) is an important tool in astronomy. The model simulates the stellar content of the Galaxy, assuming a scenario of formation and evolution. It is assumed that stars belong to 5 different populations: The thin disc, thick disc, halo, bulge and bar. It is dynamically self-consistent which delivers an advantage comparing to other stellar population synthesis models. Among other applications it can be used for data interpretation and to test different scenarios of galaxy formation and evolution. The Sloan Extension for Galactic Understanding and Exploration (SEGUE), one of the four survey’s of the sloan digital sky survey (SDSS), is a survey which covers a part of the sky and measure physical properties of stars in order to trace the structure, kinematics, and chemical evolution of the outer Milky Way disk and halo. The spectroscopic data includes for each star, temperature, gravity, metallicity (chemical abundance) and radial velocity in different directions close to the Galactic plane. We compare simulations from the Besançon Galaxy model with spectroscopic data, specifically metallicity, in order to constrain the radial metallicity gradient of the Milky Way. We use a MCMC-ABC method to fit the radial metallicity gradient in the thick disc, younger thin disc, older thin disc and their respective dispersions in metallicity. We will extend our observational data to other directions, by adding a new survey in the infrared, the Apache Point Observatory Galactic Evolution Experiment (APOGEE), such that we will be able to constrain the vertical metallicity gradient along with the radial metallicity gradient, using the same method.