Formation of ω Centauri from an Ancient Nucleated Dwarf Galaxy

Abstract

AbstractWe 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 107M⊙, 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 is orbiting the young Galactic disc in a retrograde manner with its apocenter and pericenter distances of ~ 8 kpc and ~ 1 kpc, respectively, and thus have orbital properties similar to those of ω Cen. 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 one during merging.