A number of the massive clusters in the halo, bulge and disc of the Galaxy are not genuine globular clusters (GCs), but instead are different beasts altogether. They are the remnant nuclear star clusters (NSCs) of ancient galaxies since accreted by the Milky Way. While some clusters are readily identifiable as NSCs, and can be readily traced back to their host galaxy (e.g., M54 and the Sagittarius Dwarf galaxy) others have proven more elusive. Here we combine a number of independent constraints, focusing on their internal abundances and overall kinematics, to find NSCs accreted by the Galaxy and trace them to their accretion event. We find that the true NSCs accreted by the Galaxy are: M54 from the Sagittarius Dwarf, $\omega$ Centari from Gaia-Enceladus/Sausage, NGC 6273 from Kraken and (potentially) NGC 6934 from the Helmi Streams. These NSCs are prime candidates for searches of intermediate mass black holes (BHs) within star clusters, given the common occurrence of galaxies hosting both NSCs and central massive BHs. No NSC appears to be associated with Sequoia or other minor accretion events. Other claimed NSCs are shown not to be such. We also discuss the peculiar case of Terzan 5, which may represent a unique case of a cluster-cluster merger.

中文翻译：

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银河系的吸积核团

银河系的晕、凸出和盘中的许多大质量星团并不是真正的球状星团（GC），而是完全不同的野兽。它们是自银河系吸积以来古老星系的残余核星团（NSC）。虽然一些星团很容易被识别为 NSC，并且可以很容易地追溯到它们的宿主星系（例如 M54 和人马座矮星系），但其他星团被证明更难以捉摸。在这里，我们结合了许多独立的约束，重点关注它们的内部丰度和整体运动学，以找到由银河系吸积的 NSC，并将它们追溯到它们的吸积事件。我们发现银河系吸积的真正 NSC 是：来自人马座矮人的 M54、来自盖亚土卫二/香肠的 $\omega$ Centari、来自 Kraken 的 NGC 6273 和（可能）来自 Helmi Streams 的 NGC 6934。考虑到同时拥有 NSC 和中央大质量 BH 的星系很常见，这些 NSC 是在星团内搜索中等质量黑洞 (BH) 的主要候选者。似乎没有 NSC 与红杉或其他轻微的吸积事件有关。其他声称的 NSC 显示并非如此。我们还讨论了 Terzan 5 的特殊情况，它可能代表了集群合并的独特案例。