Stirred, not shaken: Dislodging $\omega$ Centauri from the Sausage galaxy through bar resonances

Building on Laporte & Orkney's proposal that ω Centauri (ωCen) was the nuclear star cluster of the Gaia-Sausage-Enceladus (GSE) galaxy and was later dislodged by the Milky Way's bar, the authors run simulations in time-evolving bar potentials. They adopt present-day pattern speeds within Portail et al.'s Ω_b = 39 ± 3.5 km s⁻¹ kpc⁻¹ and a bar slow-down rate of Ω_dot_b = 4.5 ± 1.4 km s⁻¹ kpc⁻¹ Gyr⁻¹, tracking how bar resonances modulate the angular momentum and energies of both GSE debris and ωCen in (E, L_z) space.

They find the retrograde 3:2 resonance can produce changes ΔE ≈ 0.4×10⁵ km² s⁻² and ΔL_z ≈ 0.3–0.5×10³ km s⁻¹ kpc⁻¹ on timescales Δt ≈ 0.5–1 Gyr, well within the bar's lifespan t_bar ≈ 10–8 Gyr, and the result is independent of potential or modelling choices.

The analysis uncovers a sample of N-rich stars with metallicities −2.0 < [Fe/H] < −1.0 and aluminium enrichments consistent with ωCen. In (E, L_z) space, a map reveals a corridor of trailing N-rich stars clustered around the region connecting ωCen to the GSE debris centroid, matching ωCen's predicted past track. This is described as the best evidence yet that ωCen is the nuclear star cluster of the GSE.

Finally, using M54 and ωCen's chemistry, the authors show that neither first- nor second-generation stars follow general galaxy-wide scale chemical enrichment trends. That is empirical evidence that globular cluster chemical trends are a cluster-scale physics problem rather than a galaxy-wide one.