来自恒星形成的核星团
Nuclear Star Clusters from Clustered Star Formation
摘要：
光度不同的核星团（NSC）在晚型盘星系和球状星系中很常见。在正常恒星形成的背景下，NSC的形成是不可避免的，其中大多数恒星形成于星团中。一个年轻的，质量损失的星系团嵌入一个孤立的恒星形成星系，在一段由其初始质量和星系潮汐场决定的时间内保持引力束缚。星系团向星系中心放射状移动，如果到达中心，就会融入NSC。NSC通过吸积年轻团簇而增长的速率可以从经验团簇形成速率和溶解时间来估计。我们的模型集群迁移和溶解，发现在晚型磁盘和球体的神经干细胞可以组装从迁移集群。由此产生的恒星核包含一小部分星系的恒星质量;这部分是敏感的初始集群质量函数（ICMF）的高质量截断。由此产生的NSC质量与观测值一致，但一般来说，最终的NSC被空间上更广泛的超出外星系的向内外推指数（或Sersic）定律所包围。我们认为，过量可能与盘中的pseudoclump现象有关，尽管并非所有的pseudoclump质量都以这种方式聚集。与观察到的NSC质量的比较，可以用来约束截断质量尺度的ICMF和集群遭受迅速溶解的分数。我们推断截断质量标度为<~ 10^6 M_sun（>~ 10^5 M_sun），没有（90%）迅速溶解。
英文摘要：
Photometrically distinct nuclear star clusters (NSCs) are common in late-type-disk and spheroidal galaxies. The formation of NSCs is inevitable in the context of normal star formation in which a majority of stars form in clusters. A young, mass-losing cluster embedded in an isolated star-forming galaxy remains gravitationally bound over a period determined by its initial mass and the galactic tidal field. The cluster migrates radially toward the center of the galaxy and becomes integrated in the NSC if it reaches the center. The rate at which the NSC grows by accreting young clusters can be estimated from empirical cluster formation rates and dissolution times. We model cluster migration and dissolution and find that the NSCs in late-type disks and in spheroidals could have assembled from migrating clusters. The resulting stellar nucleus contains a small fraction of the stellar mass of the galaxy; this fraction is sensitive to the high-mass truncation of the initial cluster mass function (ICMF). The resulting NSC masses are consistent with the observed values, but generically, the final NSCs are surrounded by a spatially more extended excess over the inward-extrapolated exponential (or Sersic) law of the outer galaxy. We suggest that the excess can be related to the pseudobulge phenomenon in disks, though not all of the pseudobulge mass assembles this way. Comparison with observed NSC masses can be used to constrain the truncation mass scale of the ICMF and the fraction of clusters suffering prompt dissolution. We infer truncation mass scales of <~ 10^6 M_sun (>~ 10^5 M_sun) without (with 90%) prompt dissolution.
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