Formation of ω Centauri from an ancient nucleated dwarf galaxy in the young Galactic disc

We first present a self-consistent dynamical model in which ω Cen is formed from an ancient nucleated dwarf galaxy merging with the first generation of the Galactic thin disc in a retrograde manner with respect to the Galactic rotation. Our numerical simulations demonstrate that during merging between the Galaxy and the ω Cen’s host dwarf with MB ≃ −14 mag and its nucleus mass of 10 7 M⊙, the outer stellar envelope of the dwarf is nearly completely stripped whereas the central nucleus can survive from the tidal stripping because of its compactness. The developed naked nucleus has a very bound retrograde orbit around the young Galactic disc, as observed for ω Cen, with its apocenter and pericenter distances of ∼ 8 kpc and ∼ 1 kpc, respectively. The Galactic tidal force can induce radial inflow of gas to the dwarf’s center and consequently triggers moderately strong nuclear starbursts in a repetitive manner. This result implies that efficient nuclear chemical enrichment resulting from the later starbursts can be closely associated with the origin of the observed relatively young and metal-rich stars in ω Cen. Dynamical heating by the ω Cen’s host can transform the young thin disc into the thick disc during merging.