The oldest, most metal-poor stars in the Milky Way are unique probes of early star formation and the assembly of the Milky Way. The Galactic bulge region has typically been avoided in the search for metal-poor stars, because of the extremely high density of mostly metal-rich stars and the high dust extinction. The bulk of the Galactic bulge is thought to originate from the (early) Galactic disk. However, the oldest pressure-supported component in our Galaxy is also expected to be present in its innermost region. The most metal-poor stars in the bulge region can provide unique insights into the ancient Milky Way.
I will present results from the Pristine Inner Galaxy Survey (PIGS), which used metallicity-sensitive narrow-band CaHK photometry to identify and follow up spectroscopically thousands of metal-poor candidates in the bulge. Using the bulk PIGS radial velocities, we previously showed that the amount of inner Galaxy rotation decreases with decreasing metallicity. I will present recent work on the detailed orbital properties for all stars in PIGS, which strongly depend on their metallicities and broadly show a transition from a disky bulge to a pressure-supported component. It is exciting to see the growing amount of data on metal-poor stars in the inner regions of the Milky Way, thanks to various surveys, allowing us to set important constraints on the formation of the ancient inner Galaxy.
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