Periodic Reporting for period 1 - TEMPOS (Temporal Evolution of the Milky-way Properties from an Observational and theoretical Sinergy)
Période du rapport: 2023-09-01 au 2025-11-30
Understanding how galaxies form and evolve in the Universe is a key, long-term goal of Astrophysics. In this regard, our Galaxy provides unique insights because, due to its proximity, detailed galactic properties can be resolved that can unravel its formation history. For this reason, the international community and in particular European countries have made large investments in observational resources to perform Galactic research during this and the following decades (for example the Gaia mission and a number of ambitious spectroscopic surveys like WEAVE and 4MOST, among others). The extraordinary wealth of data is facilitating an unprecedented leap forward to uncover the origin and evolution of our Galaxy, with important implications for deciphering the physical processes governing galaxy evolution in general. In the last decade, there has been important progress in the understanding of the chemo-dynamical and accretion history of the Milky Way. There is, however, an important caveat in observational analysis: the lack of a methodology to derive precise stellar ages for large, unbiased samples of stars. Without the temporal dimension it is difficult to interpret observed Galactic stellar properties in terms of the processes that led to the current configuration of the Galaxy. This proposal aims to develop and exploit a novel methodology to derive precise age distributions for Milky-Way (MW) stellar populations. These age distributions will be combined with the chemo-dynamical information provided by the huge spectroscopic datasets and analysed using chemical evolution models. Altogether, this information will provide key strong constraints to evaluate theoretical models of galaxy formation and evolution, thus approaching the study of our Galaxy through a comprehensive observational and theoretical approach.
The activities carried out within the TEMPOS projects can be summarised as follows.
We established the foundations for applying the CMD-fitting technique to Milky Way data, in particular by:
- Incorporating a more complete and up-to-date dust map to account for extinction by the interstellar medium, thereby improving the performance of the methodology across the Galactic disc;
- Developing a tool to quantify the completeness of stellar populations within a given Galactic volume, allowing us to account for missing stars caused by selection effects.
Using this framework, we inferred the age–metallicity relation of the kinematically selected thin and thick discs of the Milky Way within a local volume around the Sun with unprecedented detail. The establishment of this methodology also enabled the determination of the age–metallicity relation of the Gaia–Sausage–Enceladus remnants, as well as the interpretation of the presence of metal-rich stars in the solar neighbourhood through comparisons with cosmological simulations. Ongoing work focuses on constraining the mass of gas required to form the Milky Way thick disc by comparison with chemical evolution models.
We established the foundations for applying the CMD-fitting technique to Milky Way data, in particular by:
- Incorporating a more complete and up-to-date dust map to account for extinction by the interstellar medium, thereby improving the performance of the methodology across the Galactic disc;
- Developing a tool to quantify the completeness of stellar populations within a given Galactic volume, allowing us to account for missing stars caused by selection effects.
Using this framework, we inferred the age–metallicity relation of the kinematically selected thin and thick discs of the Milky Way within a local volume around the Sun with unprecedented detail. The establishment of this methodology also enabled the determination of the age–metallicity relation of the Gaia–Sausage–Enceladus remnants, as well as the interpretation of the presence of metal-rich stars in the solar neighbourhood through comparisons with cosmological simulations. Ongoing work focuses on constraining the mass of gas required to form the Milky Way thick disc by comparison with chemical evolution models.
These results reveal clearly distinct age–metallicity relations for the thick and thin discs of the Milky Way, with a pronounced transition occurring around 10 Gyr ago. This novel finding establishes a connection between the transition from thick- to thin-disc–like stellar kinematics and the epoch of the last major merger experienced by the Milky Way, the Gaia–Sausage–Enceladus event.
Furthermore, the high precision achieved in the inferred age and metallicity distributions uncovers fine structure that places new constraints on the star formation history and evolutionary pathways of the Galactic disc. In particular, we identify a previously unrecognised population of very old, very metal-poor stars on thin-disc–like orbits.
This project laid the groundwork for applying CMD fitting to other chemo-dynamically selected Milky Way stellar populations.
Furthermore, the high precision achieved in the inferred age and metallicity distributions uncovers fine structure that places new constraints on the star formation history and evolutionary pathways of the Galactic disc. In particular, we identify a previously unrecognised population of very old, very metal-poor stars on thin-disc–like orbits.
This project laid the groundwork for applying CMD fitting to other chemo-dynamically selected Milky Way stellar populations.