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 omega 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 omega Cen host dwarf with M-B similar or equal to -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 omega Cen, with apocentre and pericentre distances of similar to8 and similar to1 kpc, respectively. The Galactic tidal force can induce radial inflow of gas to the centre of the dwarf 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 omega Cen. Dynamical heating by the omega Cen host can transform the young thin disc into the thick disc during merging.