Bar-induced migration of $\omega$ Centauri away from Gaia Sausage-Enceladus

Abstract

The globular cluster $\omega$ Cen has been suggested to have originated in the Gaia Sausage-Enceladus (GSE) merger event, possibly as its nuclear star cluster. However, the present-day orbits of $\omega$ Cen and the GSE debris are very different. We investigate the scenario in which $\omega$ Cen originated in the GSE and migrated to its current position due to perturbations from the Galactic bar. The [$\alpha$/M] distributions of stars located between the GSE debris and $\omega$ Cen in $(L_z,E)$ space tentatively support this scenario, but are not conclusive. We run simulations of the GSE debris and $\omega$ Cen in a realistic Milky Way potential with a decelerating bar at various present-day pattern speeds. We find that $\omega$ Cen can indeed be traced back to the phase space region occupied by the GSE debris. However, this would likely require a pattern speed of $\Omega_\mathrm{b}\lesssim26$ km s$^{-1}$ kpc$^{-1}$, which is much lower than most recent estimates. We conclude that a GSE origin for $\omega$ Cen is dynamically and chemically plausible, but only with a re-evaluation of the current consensus on the bar's pattern speed.