Effects of initial density profiles on massive star cluster formation in giant molecular clouds
Effects of initial density profiles on massive star cluster formation in giant molecular clouds
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DOI：
10.1093/mnras/stab491
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发表时间：
2020-05
影响因子：
4.8
通讯作者：
Yingtian Chen;Hui Li;M. Vogelsberger
中科院分区：
文献类型：
--
作者：
Yingtian Chen;Hui Li;M. Vogelsberger
我们进行了一套流体动力学模拟，以研究如何初始密度分布的巨分子云（GMC）影响其随后的演变。我们发现整个星云的星星形成持续时间和整体星星形成效率对不同剖面的选择并不敏感，而主要受引力坍缩和恒星反馈的相互作用所控制。尽管有这种相似性，但不同轮廓的GMC显示出截然不同的星星形成模式。对于较浅的剖面，GMC首先分裂成许多自引力核心，并形成分布在整个云层中的子集群。这些子集群后来被“分层”组装成中心集群。相比之下，对于陡峭的轮廓，一个巨大的集群迅速形成在云的中心，然后通过气体吸积逐渐增加其质量。因此，从云层中出现的中央星团具有较浅的轮廓，质量较低，旋转也比那些具有陡峭轮廓的星团小。这是因为：1）在较浅的剖面中，质量和角动量的很大一部分存储在子集群的轨道运动中，这些子集群不能合并到中心集群中; 2）在较浅的剖面中，频繁的分层合并通过剧烈的弛豫和潮汐破坏导致质量和角动量的进一步损失。令人鼓舞的是，在陡峭的配置文件的集群旋转的程度是一致的，最近观察到的年轻和中年集群。我们推测，旋转的球状星团很可能是通过早期宇宙中集中云的“吸积”模式形成的。
We perform a suite of hydrodynamic simulations to investigate how initial density profiles of giant molecular clouds (GMCs) affect their subsequent evolution. We find that the star formation duration and integrated star formation efficiency of the whole clouds are not sensitive to the choice of different profiles but are mainly controlled by the interplay between gravitational collapse and stellar feedback. Despite this similarity, GMCs with different profiles show dramatically different modes of star formation. For shallower profiles, GMCs first fragment into many self-gravitation cores and form sub-clusters that distributed throughout the entire clouds. These sub-clusters are later assembled ``hierarchically'' to central clusters. In contrast, for steeper profiles, a massive cluster is quickly formed at the center of the cloud and then gradually grows its mass via gas accretion. Consequently, central clusters that emerged from clouds with shallower profiles are less massive and show less rotation than those with the steeper profiles. This is because 1) a significant fraction of mass and angular momentum in shallower profiles is stored in the orbital motion of the sub-clusters that are not able to merge into the central clusters 2) frequent hierarchical mergers in the shallower profiles lead to further losses of mass and angular momentum via violent relaxation and tidal disruption. Encouragingly, the degree of cluster rotations in steeper profiles is consistent with recent observations of young and intermediate-age clusters. We speculate that rotating globular clusters are likely formed via an ``accretion'' mode from centrally-concentrated clouds in the early Universe.