Formation and evolution of the Milky Way and the local group

(G. Casali, L. Magrini, E. Pancino, S. Randich, M. Tsantaki, M. Van der Swaelmen)

Galactic archaeology aims at investigating the structure and evolution of our Galaxy by measuring ages and chemical compositions in different stellar populations of our own Galaxy, which can be considered as a benchmark to understand disk galaxies. The Milky Way is indeed the only galaxy in which we can study in detail the resolved stellar population, from white dwarfs to super giants, allowing to reconstruct its complete star formation history in time and in space.

Galactic archaeology is living in a golden age thanks to the data collected by the Gaia satellite, complemented by large ongoing spectroscopic surveys, such as Gaia-ESO (Randich & Gilmore 2013), APOGEE (Majewski et al. 2017), GALAH (De Silva et al. 2015) and LAMOST (Cui et al. 2012), and future spectroscopic surveys and instruments (e.g., WEAVE, MOONS, 4MOST, MSE). The combination of these data is providing a new multi-dimensional view of the structure and evolution of our Galaxy.

In particular, the wide variety of elemental abundances and abundance ratios in the different populations of our Galaxy provides fundamental constraints on the scenarios of Galaxy formation and evolution. At the same time, they provide fundamental constraints on stellar evolution and nucleosynthesis (see, e.g. Magrini et al. 2018A, 2018B.

Our group constitutes, with the Institute of Astronomy of Cambridge, the core of the Gaia-ESO survey team. The Gaia-ESO survey has been the first large high-resolution spectroscopic survey of all Milky Way components (340 observing nights on the ESO-VLT). It used FLAMES to target 10⁵ field stars in the bulge, the thick and the thin discs, and the halo, as well as a significant sample of open star clusters, providing a homogeneous overview of the distributions of kinematic, metallicity, and elemental abundances.

The Gaia-ESO has put a special emphasis on OCs, in order to address a variety of science goals, including cluster formation and dynamical evolution, stellar physics, and thin disc formation and evolution. An example of one of the main goals of the Gaia-ESO survey is the determination of the radial metallicity gradient in the thin disc of the Milky Way (e.g., Jacobson et al. 2016, Spina et al. 2017, Randich 2020 , a fundamental constraint to understand the formation scenario of our Galaxy.

Thanks to the experience gained with Gaia-ESO, our group is now involved in most of the forthcoming spectroscopic surveys and instruments, as WEAVE, MOONS, MSE, and MAVIS.

Figure 1: Artist’s impression of the Gaia-ESO survey, which combines spectroscopic observations from the ground (VLT) with astrometric observations from space (Gaia, 2013-2018). Credit: ESA/ESO