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arXiv 1002.1325astro-ph.GAastro-ph.CO
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球状星团金属丰度分布的模拟

Modeling the Metallicity Distribution of Globular Clusters

Alexander L. Muratov, Oleg Y. Gnedin

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matches version accepted by ApJ
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摘要：

观测到的球状星团的金属丰度反映了它们高红移宿主星系的星际介质的物理条件。大多数大型星系中的球状星团系统显示出双峰的颜色和金属丰度分布，这通常被解释为表明团簇形成的两种不同模式。富金属和贫金属星系团在其宿主星系中具有系统性的不同位置和运动学。然而，红色和蓝色星团具有相似的内部性质，例如质量，大小和年龄。因此，有趣的是，探索是否富金属和贫金属的集群可以形成一个共同的机制，仍然是符合双峰分布。我们提出了这样一个模型，它规定形成的球状星团半分析使用星系组装历史的宇宙学模拟再加上观测到的比例关系的数量和金属量的冷气体可用于恒星形成。我们假设大质量的星团只形成在合并的大规模的富含气体的星系和调整模型参数，以重现在银河系中观察到的分布。一个广泛的，但不是全部的，范围内的模型实现产生的金属丰度分布与数据一致。我们发现，早期合并的较小的主机创建专门的蓝色集群，而随后合并的更大的星系创建红色和蓝色集群。因此，双峰性是少数晚期大规模合并事件的自然结果。这一结论并没有受到我们对高红移星系中恒星质量和冷气体质量的知识的巨大不确定性的显著影响。锁定在球状星团中的银河系恒星质量的比例从z>3时的10%以上下降到目前的0.1%。

英文摘要：

Observed metallicities of globular clusters reflect physical conditions in the interstellar medium of their high-redshift host galaxies. Globular cluster systems in most large galaxies display bimodal color and metallicity distributions, which are often interpreted as indicating two distinct modes of cluster formation. The metal-rich and metal-poor clusters have systematically different locations and kinematics in their host galaxies. However, the red and blue clusters have similar internal properties, such as the masses, sizes, and ages. It is therefore interesting to explore whether both metal-rich and metal-poor clusters could form by a common mechanism and still be consistent with the bimodal distribution. We present such a model, which prescribes the formation of globular clusters semi-analytically using galaxy assembly history from cosmological simulations coupled with observed scaling relations for the amount and metallicity of cold gas available for star formation. We assume that massive star clusters form only during mergers of massive gas-rich galaxies and tune the model parameters to reproduce the observed distribution in the Galaxy. A wide, but not entire, range of model realizations produces metallicity distributions consistent with the data. We find that early mergers of smaller hosts create exclusively blue clusters, whereas subsequent mergers of more massive galaxies create both red and blue clusters. Thus bimodality arises naturally as the result of a small number of late massive merger events. This conclusion is not significantly affected by the large uncertainties in our knowledge of the stellar mass and cold gas mass in high-redshift galaxies. The fraction of galactic stellar mass locked in globular clusters declines from over 10% at z>3 to 0.1% at present.

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