Formation of Omega Centauri by Tidal Stripping of a Dwarf Galaxy

Abstract

We have investigated whether or not a tidal stripping scenario can reproduce the observed surface-brightness profile of omega Centauri using N-body simulations. Assuming that the progenitor of omega Centauri is a dwarf elliptical galaxy, we model it with a King model with a core radius being the same as that of omega Centauri. A dark matter halo of the dwarf is not taken into account. We consider two different models of the Milky Way potential: a singular isothermal sphere and a three-component model. The progenitor dwarf is expressed as an N-body system, which orbits in the fixed Galactic potential. The dwarf lost more than 90 per cent of its mass during the first few pericenter passages. Thereafter, the mass remains practically constant. The final surface-density profile is in good agreement with the observational data on omega Centauri, if the pericenter distance of the orbit of the progenitor dwarf is around 500 pc. This value is within the error bar of the current proper motion data on omega Centauri and Galactic parameters. Although our simulation is limited to a King-like progenitor dwarf without a dark matter halo, it strongly suggests that the current density profile of omega Centauri is nicely reproduced by a tidal stripping scenario, in other words, that omega Centauri can plausibly be identified with a stripped dwarf elliptical.