41) The history of the Galactic disc and halo from Gaia DR2 colour-magnitude diagrams

Abstract: Gaia DR2 has provided distances and photometry, and thus colour-magnitude diagrams in the absolute plane, for stars over an unprecedented vast volume in the Milky Way, encompassing significant fractions of the thin and thick disk, and halo. This has allowed us, for the first time, to derive unprecedentedly detailed star formation histories from direct modelling of these colour-magnitude diagrams, using the same techniques that have been proven successful for external galaxies in the Local Group. Our first results for a volume of 2 Kpc radius from the Sun are extraordinarily promising. They have allowed us to date the first events involved in the formation of the inner Milky Way halo (with kinematic selection of halo/Gaia-Enceladus stars), as well as to retrieve the early star formation history of the thick disk (Gallart et al. 2019, NatAstro) and to determine the presence of epochs of enhanced star formation well constrained in time, that can be associated to the various pericentric passages of the Sagittarius dwarf galaxy (Ruiz-Lara et al. 2020, NatAstro). Additionally, we have obtained results of unprecedented clarity regarding the vertical distribution of ages in the Milky Way disk (Gallart et al. 2020, in prep). I will discuss these results as well as future prospects to combine chemodynamical information from spectroscopic surveys and to reach a larger Milky Way volume with this new approach to study the Milky Way evolutionary history.

Bio: Carme Gallart is currently a Research Professor at Instituto de Astrofísica de Canarias (Tenerife, Spain). She obtained her PhD at University of La Laguna/Instituto de Astrofisica de Canarias in 1996. After that she was a postdoc at Carnegie Observatories (1996-1998) and at Yale U. (1999-2001). In 2002 she returned to the IAC with a Ramón y Cajal fellowship, and since 2005 she is a member of its permanent research staff. Her main research interests are stellar populations and star formation and chemical enrichment histories in Local Group galaxies. She has been one of the pioneers of the CMD fitting technique for determination of star formation histories. She is now leading a research line aimed at exploiting Gaia data to unravel de formation and evolution of the Milky Way components, through the analysis of the Gaia color-magnitude diagrams.