Le 19 octobre 2018
De 10h30 à 12h00
Payel Das
Oxford
Galaxy evolution seeks to understand how the featureless groups of stars in the early Universe metamorphosed into the diverse range of morphologies that can be observed today. There are a number of drivers acting on different scales. The interstellar scale includes processes such as star formation, explosions of massive stars, and dynamical interactions between stars. On a larger scale, collisions between nearby galaxies serve to reshape the distribution of stars as well as deposit alien stars from satellite galaxies in the outer haloes. The haloes of dark matter that enshroud all galaxies futher modulate the rate of star formation and collision events. The arrival of the second data release of Gaia together with a number of ground-based spectroscopic surveys has provided six-dimensional phase-space coordinates, metallicity, and chemical abundances for an unprecedented number of stars in the Milky Way. This has led to a dramatic revolution in the emerging field of ‘galactic archaeology’, which uses individual stars to probe past evolutionary processes in detail. One fundamental stellar quantity that needs to be estimated for galactic archaeology studies is age. I will present a new catalogue of ~3 million ages for Milky Way stars that uses a novel machine-learning method for estimating ages of red giants. I will also present a sophisticated tool for creating chemodynamical models called an ‘extended distribution function’, or EDF. This is foremost a model that is in dynamical equilibrium and therefore encodes the gravitational potential and orbital structure of the Milky Way. It furthermore describes the distribution of stellar ages, metallicities, and alpha abundances enabling me to explore the star formation history, chemical enrichment, and secular heating in the Milky Way discs and the assembly history of the stellar halo.