Where's Waldo? Unveiling a metal-poor extension of the Milky Way thin disc with Pristine-Gaia-synthetic

Our understanding of the Milky Way’s formation history can be refined by analyzing the information encoded in its oldest stellar populations, typically their chemical composition and orbital motion. Having access to such properties is valuable to depict a larger picture of the earliest stages of galactic formation. With the rise of Gaia, an orbital characterization of the different components of our Galaxy has been built over the years, leading to the discovery of various substructures questioning the formation processes at stake. In that context, following previous work (Fernández-Alvar et al. 2021), we studied the presence of a metal-poor extension of the thin disc, using photometric metallicities from the Pristine survey (Starkenburg et al. 2017). Combining Gaia astrometry with Pristine photometry, we recovered two stellar populations at -2 < [Fe/H] < -1.5 : one slow-rotating (halo-like) and one fast-rotating (thin disc-like) in the MW anticentre using Gaussian mixture models coupled with a Markov-Chain-Monte-Carlo approach. We pursued our investigation with the upcoming Pristine-Gaia-synthetic catalog (Martin et al. 2023, in prep.), which gathers 1.7 million metal-poor stars with metallicities inferred from BP/RP spectrophotometry. Our aim is to make use of this statistically significant catalog to characterize the kinematic behavior of the metal-poor MW population in a larger field of view. In this talk, I will present some preliminary results investigating the rotating metal-poor Milky Way using 3D kinematics of this all-sky sample

The Pristine survey -- XXIII. Data Release 1 and an all-sky metallicity catalogue based on Gaia DR3 BP/RP spectro-photometry

We use the spectro-photometric information of ~219 million stars from Gaia's DR3 to calculate synthetic, narrow-band, metallicity-sensitive CaHK magnitudes that mimic the observations of the Pristine survey, a survey of photometric metallicities of Milky Way stars that has been mapping more than 6,500 deg^2 of the northern sky with the CFHT since 2015. These synthetic magnitudes are used for an absolute re-calibration of the deeper Pristine photometry and, combined with broadband Gaia information, synthetic and Pristine CaHK magnitudes are used to estimate photometric metallicities over the whole sky. The resulting metallicity catalogue is accurate down to [Fe/H]~-3.5 and is particularly suited for the exploration of the metal-poor Milky Way ([Fe/H]<-1.0). We make available here the catalogue of synthetic CaHK_syn magnitudes for all stars with BP/RP information in Gaia DR3, as well as an associated catalogue of more than ~30 million photometric metallicities for high S/N FGK stars. This paper further provides the first public DR of the Pristine catalogue in the form of higher quality recalibrated Pristine CaHK magnitudes and photometric metallicities for all stars in common with the BP/RP information in Gaia DR3. We demonstrate that, when available, the much deeper Pristine data greatly enhances the quality of the derived metallicities, in particular at the faint end of the catalogue (G_BP>16). Combined, both catalogues include more than 2 million metal-poor star candidates as well as more than 200,000 and ~8,000 very and extremely metal-poor candidates. Finally, we show that these metallicity catalogues can be used efficiently, among other applications, for Galactic archaeology, to hunt for the most metal-poor stars, and to study how the structure of the Milky Way varies with metallicity, from the flat distribution of disk stars to the spheroid-shaped metal-poor halo. (Shortened)Comment: 30 pages, 24 figures, submitted to A&A. First two authors are co-first author. The CaHK photometry catalogue and the two photometric metallicity catalogues are available, before acceptance, as large compressed csv files at: https://seafile.unistra.fr/d/ee0c0f05719d4368bcbb