Formation of ω Centauri from an Ancient Nucleated Dwarf Galaxy

By Kenji Bekki, Kenneth C. Freeman. 2003

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We 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 M B ⋍ ‒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 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.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/ba4bd2a36d353bc67e504e8f639d26045eb61ead

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Citations in the corpus

Multiple populations in globular clusters (2012, background): “(2007): the globular clusters must have been initially a large factor (10-100) more massive than today and almost all the first generation stars must have been preferentially lost.”
Evidence for two early accretion events that built the Milky Way stellar halo (2019, background): “Already Freeman (1993) and Bekki & Freeman (2003) suggested it is the nucleus of a stripped dwarf galaxy, inspired by its very bound retrograde orbit.”
Nuclear star clusters (2009, background): “…Milky Way globular clusters The brightest, most massive globular clusters in the Milky Way, ωCen has long been suspected to be a former NSC (e.g., Bekki and Freeman 2003), due to its large spread in metallicity (e.g., Norris et al. 1996; Johnson and Pilachowski 2010), and possibly also an age…”
Two distinct halo populations in the solar neighborhood. II. Evidence from stellar abundances of Mn, Cu, Zn, Y, and Ba (2011, background): “Given that the ωCen globular cluster is probably the nucleus of a dwarf galaxy (e.g. Bekki & Freeman 2003), and that many of the low-α stars have a V-velocity component similar to that of ωCen, it is possible that a significant fraction of the low-α halo stars in the solar neighborhood have been…”
Accreted versus in situ Milky Way globular clusters (2010, methodology): “According to the best fit models of Bekki & Freeman (2003), the progenitor dwarf galaxy had a luminosity of MV ∼ –14.5.”
Masses of Star Clusters in the Nuclei of Bulgeless Spiral Galaxies (2004, background): “This scenario has been proposed for ω Cen (see e.g. Bekki & Freeman 2003 and references therein), G1 orbiting M31 (e.g. Meylan et al. 2001), the ultra compact dwarf galaxies in the Fornax cluster (Drinkwater et al. 2003) and others.”
The formation and assembly history of the Milky Way revealed by its globular cluster population (2018, background): “This suggests the existence of more than one progenitor (of which the retrograde one likely had NGC 5139/ωCen as its nuclear cluster, cf. Bekki & Freeman 2003), but the lack of structure in the satellite branch does not enable us to distinguish these.”
Comparing the properties of local globular cluster systems: implications for the formation of the Galactic halo (2004, background): “Ithas been suggested thatω Cen is the surviving nucleus of a dwarf galaxy accreted and stripped by the Galaxy (see e.g., Bekki & Freeman (2003), and references therein).”