ChronoGal · Chronology of our Galaxy from Gaia Color-Magnitude Diagram fitting

The overarching goal of ChronoGal is to unveil the sequence of events and physical processes that have shaped the Milky Way (MW) from its early assembly to the present, by providing the holy grail of Galactic Archaeology (GA): precise age information. Our Galaxy is key to study disk galaxy formation and evolution, as it can be analyzed in exceptional detail using individual stars carrying the fossil record of its entire evolution. The importance of GA is underscored by the vast resources invested in it: Gaia parallaxes, homogeneous photometry, proper motions and velocities have transformed the field, aided by a huge effort from ambitious ground-based spectroscopic surveys.Despite spectacular recent progress, GA is nearing an impasse due to the lack of precise ages for large, unbiased stellar samples, which are critical for determining our Galaxy’s chronology. My unique expertise allows me to tackle this key issue by including color-magnitude diagram fitting in the field’s toolbox. Previously limited to studying external Local Group galaxies, this technique can finally now be applied to our Galaxy, providing unprecedentedly precise and homogeneous age-metallicity distributions for hundredths of millions of stars across all MW components. This is made possible by the accurate Gaia-based distances.ChonoGal’s ages will provide clear answers to persistent questions on MW evolution. Crucially, ChronoGal will precisely date the disk emergence, determine the duration of the enigmatic thick disk phase, resolve the debate on the presence of intermediate-age stars in the bulge, reconstruct the major halo building blocks and pinpoint the accretion time of these fossils of high-redshift dwarf galaxies. This will clarify the impact of mergers on shaping the stellar content and morphology of disk galaxies. This ambitious and urgent project, with Gaia DR4 in 2026, will be transformative, providing the reliable and precise ages needed to advance our MW understanding.