Letters of Intent received in 2021

LoI 2023-2155
Linking near- and far-field galaxy formation with precise ages of stars and stellar populations

Topics

- Precision and accuracy of age indicators: from nearby stars to unresolved stellar populations and cosmic chronometers

- Successes and shortcoming of stellar models in the light of astrometric and asteroseismic constraints; how systematic uncertainties in predicting the evolution of single and binary stars propagate to the ages of (un)resolved stellar populations

- The Milky Way “rediscovered”: assembly history of the MW as seen by Gaia, large spectroscopic surveys, asteroseismology and CMD fitting

- The Milky Way in context, how does our picture of the early assembly history of the MW compares with inference from high-redshift galaxies (especially with JWST) and cosmological simulations?

- Define a roadmap for future coordinated efforts and links between communities

Rationale

Understanding how galaxies formed and evolved within the context of the concordance cosmological model is being pursued on three fronts: observations of objects seen at high redshifts and early times, simulations of clustering matter and star formation, and detailed observation of the interplay between the chemistry and dynamics of stars in the Milky Way and in local-group galaxies. Major progress has happened in all these three fronts calling for a comparison between the evolution implied by the snapshots of distant galaxies through time, that implied by the archeological record of our Galaxy, and that occurring in numerical simulations.

The Milky Way is a complex system, with dynamical and chemical substructures, where several competing processes such as mergers, internal secular evolution, gas accretion and gas flows take place. A detailed view of how such a giant spiral galaxy was formed and evolves is now at hand, thanks to the availability of unprecedented datasets on the kinematics and chemical abundances of millions of stars. Crucially, these data are complemented by improved age-dating techniques (CMD fitting, asteroseismology) enabling a time-resolved picture of the Galaxy. Sophisticated techniques and datasets also allow inferences on star-formation histories of (un)resolved stellar populations in a growing set of galaxies.

A comprehensive picture of the extragalactic universe is also emerging. In the near term, JWST will measure the abundance, star formation, and chemical properties of Milky Way progenitors to z > 10, as well as the likely source and epoch of reionisation. Deep photometric surveys now and in the future (Rubin Observatory, Euclid) are measuring the merging fractions and low-surface brightness stellar halos for an unprecedented range and number of galaxies. Numerical simulations have continued to show the importance of internal feedback effects such as AGN and supernova heating.

It is now time to link the combined weight of this picture to the Galaxy, to elucidate the interplay between the various physical processes at play in galaxy formation, and to exchange knowledge across communities about the opportunities and limitations stemming from the wealth of novel datasets and models available.