Origin of the very metal poor stars in the disk of the Milky Way

Abstract

The stars with quasi-primordial chemistry are remnants of the early stages of formation of our Galaxy thus providing insights into its assembly. We use GARROTXA, a “Milky Way-like” high resolution zoom-in cosmological simulation, to show that even though these stars are commonly associated with the halo of the Galaxy, by setting geometrical and dynamical constraints we managed to detect 619 ultra metal-poor stars with planar orbits that show a slight preference for prograde motion (around ∼ 7% above the expected value of 0.5). The fraction of ultra metal-poor prograde orbits that we find is smaller than in other simulations of previous studies and than the observed fraction in the Milky Way. Moreover, we traced those stars back to our earliest available snapshot (t = 1.87 Gy after the Big Bang) and proved that all of them (except two) belonged to the primordial blocks from which the proto-galaxy was formed. Finally, we conclude that low metallicity stars are excellent indicators about the history of formation and assembly of its galaxy