The Galactic underdogs: characterizing a population of metal-poor stars with disc kinematics in the Milky Way

Gonzalez Rivera, Isaure; Hill, Vanessa; Kordopatis, Georges; Gran, Felipe; Fernandez-Alvar, Emma
Bibliographical reference

EAS2024

Advertised on:
7
2024
Number of authors
5
IAC number of authors
1
Citations
0
Refereed citations
0
Description
To deepen our knowledge of the early history of the Milky Way, it is of particular interest to investigate the orbital and chemical properties of the most metal-poor stars, which are commonly associated with the oldest stars in our Universe. With the advent of astrometric (Gaia), spectroscopic (APOGEE, GALAH, LAMOST, Gaia-RVS), and photometric surveys (Pristine), there is a great opportunity to answer crucial questions related to disc formation, which still remains today a puzzling assembly process. In that context, following the work of the Pristine collaboration (Starkenburg et al. 2017, Fernandez-Alvar et al. 2021, Sestito et al. 2019, 2021, Zhang et al. 2023), and many recent authors (Bellazzini et al. 2023, Li et al. 2023, Hong et al. 2023, Sotillo-Ramos et al. 2023), we aim at characterizing a population of metal-poor stars ([Fe/H] < -1.5 dex) with disc-like orbits, namely planar and prograde with high angular momenta. Using the invaluable information contained in Gaia DR3 BP/RP spectra, Martin et al. (2023) released the Pristine-Gaia synthetic catalog of photometric metallicities, that we combine with Gaia DR3 astrometry to build a sample of ~ 3M giant stars with chemo-dynamical information. First, we focus on assessing the robustness of Pristine-Gaia synthetic metallicities validating and curating the sample for our use with the help of spectroscopic surveys. We are able to identify an asymmetric angular momentum distribution within our sample, down to the lowest metallicities ([Fe/H] < -1.7), in favor of a prograde component. We then investigate whether the population could be due to the tail of a zero-rotation or a prograde halo, investigating Vφ and action space distributions in different metallicity ranges. Finally, we discuss potential origins for this population in the light of recent works (bar or accreted population, prograde halo,...).