The Pristine Inner Galaxy Survey (PIGS) – V. A chemo-dynamical investigation of the early assembly of the Milky Way with the most metal-poor stars in the bulge

Abstract

The investigation of the metal-poor tail in the Galactic bulge provides unique information on the early Milky Way assembly and evolution. A chemo-dynamical analysis of 17 very metal-poor stars (VMP, [Fe/H]<−2.0) selected from the Pristine Inner Galaxy Survey was carried out based on Gemini/GRACES spectra. The chemistry suggests that the majority of our stars are very similar to metal-poor stars in the Galactic halo. Orbits calculated from Gaia EDR3 imply these stars are brought into the bulge during the earliest Galactic assembly. Most of our stars have large [Na,Ca/Mg] abundances, and thus show little evidence of enrichment by pair-instability supernovae. Two of our stars (P171457, P184700) have chemical abundances compatible with second-generation globular cluster stars, suggestive of the presence of ancient and now dissolved globular clusters in the inner Galaxy. One of them (P171457) is extremely metal-poor ([Fe/H]<−3.0) and well below the metallicity floor of globular clusters, which supports the growing evidence for the existence of lower-metallicity globular clusters in the early Universe. A third star (P180956, [Fe/H]∼−2) has low [Na,Ca/Mg] and very low [Ba/Fe] for its metallicity, which are consistent with formation in a system polluted by only one or a few low-mass supernovae. Interestingly, its orbit is confined to the Galactic plane, like other very metal-poor stars found in the literature, which have been associated with the earliest building blocks of the Milky Way.

Very Metal-poor Stars in the Solar Vicinity: Kinematics and Abundance Analysis

“…All our stars having measurements for both elements occupy the expected region for halo stars. At odds with globular clusters' stars, our sample stars do not show any Al-Mg anticorrelation(Lucey et al 2022;Sestito et al 2023).…”

Discovery of a New Local Group Dwarf Galaxy Candidate in UNIONS: Boötes V

“…A Monte Carlo randomization has been performed to infer the T eff , logg, and their uncertainties. These methods have proved to yield robust stellar parameters compatible with high-resolution spectroscopic values in the very metal-poor regime (e.g., Kielty et al 2021;Sestito et al 2023;Waller et al 2023). We derive T eff = 4481± 77 K and logg = 0.87± 0.11, and incorporate these parameters into the synthetic spectrum.…”

The Pristine Inner Galaxy Survey (PIGS) – VI. Different vertical distributions between two DIBs at 442.8 nm and 862.1 nm

“…The PIGS (Arentsen et al 2020b(Arentsen et al , a , 2021 is an extension of the Pristine surv e y, which uses the metallicity-sensitiv e narrow-band CaHK filter on the Canada-France-Hawaii-Telescope (CFHT) to search for and study the most metal-poor stars (Starkenburg et al 2017 ). PIGS aims at obtaining spectra for the metal-poor stars in the Galactic bulge and studying their kinematics (Arentsen et al 2020a ), as well as the chemical and dynamical evolution of the inner Galaxy (Arentsen et al 2020b(Arentsen et al , 2021Sestito et al 2022 ). The PIGS targets were selected with a magnitude limit of 13 .…”