paper

Galaxy mass dependence of metal-enrichment of nuclear star clusters

arXiv:2412.03132 · doi:10.3847/1538-4357/ad9b0d

Abstract

Nuclear Star Clusters (NSCs) are commonly found in galaxy centers, but their dominant formation mechanisms remain elusive. We perform a consistent analysis of stellar populations of 97 nearby NSCs, based on VLT spectroscopic data. The sample covers a galaxy stellar mass range of 10 to 10 M and is more than 3 larger than any previous studies. We identify three galaxy stellar mass regimes with distinct NSC properties. In the low-mass regime of 8.5, nearly all NSCs have metallicities lower than circum-NSC host but similar to typical red globular clusters (GCs), supporting the GC inspiral-merger scenario of NSC formation. In the high-mass regime of 9.5, nearly all NSCs have higher metallicities than circum-NSC host and red GCs, suggesting significant contributions from in-situ star formation (SF). In the intermediate-mass regime, a comparable fraction of NSCs have higher or lower metallicities than circum-NSC host and red GCs, with no clear dependence on NSC mass, suggesting intermittent in-situ SF. The majority of NSCs with higher metallicities than their host exhibit a negative agemetallicity correlation, providing clear evidence of long-term chemical enrichment. The average NSChost metallicity difference peaks broadly around and declines towards both higher and lower galaxy mass. We find that the efficiency of dynamical friction-driven inspiral of GCs observed in present-day galaxies can explain the NSC mass at but falls short of observed ones at higher galaxy mass, reinforcing our conclusions based on stellar population analysis.

arXiv comment34 pages, 12 figures, accepted for publication in ApJ

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