Searching for globular cluster-like abundance patterns in young massive clusters - II. Results from the Antennae galaxies
Searching for globular cluster-like abundance patterns in young massive clusters - II. Results from the Antennae galaxies
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DOI：
10.1093/mnras/stx628
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发表时间：
2017-03
影响因子：
4.8
通讯作者：
C. Lardo;I. Cabrera-Ziri;B. Davies;N. Bastian
中科院分区：
文献类型：
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作者：
C. Lardo;I. Cabrera-Ziri;B. Davies;N. Bastian
在年龄大于6 Gyr的星系团中，存在具有独特轻元素丰度的多个种群（MP）是一种普遍现象。质量、光度和大小与古代球状星团相当的星团至今仍在形成。尽管如此，存在的轻元素的变化已经很差的调查，在这样年轻的系统，即使知识的年龄，这种现象的发展是至关重要的理论模型的MP。我们使用的J-波段集成光谱的三个年轻的（7-40万年）在NGC 4038集群寻找铝的变化指示MP。假设绝大多数（>70%）的恒星都具有高铝含量的特征-就像在质量相当的星系团中观察到的那样;我们发现没有一个研究的星系团显示出显著的铝变化。在近红外波段观测到的所有六个年轻星系团中都测量到了小的Al扩散。虽然这是不太可能的，年轻的集群只显示低铝，而老的显示不同程度的铝变化，这表明MP是不存在的可能性，在这样年轻的年龄，至少在高质量的恒星组成部分。或者，具有类场化学性质的恒星比例可能非常大，在综合光谱中模仿低Al丰度。最后，由于年轻星团的近红外恒星连续体几乎完全是由于发光的红超巨星，我们也可以推测MP只表现在低质量恒星由于一些进化机制。
The presence of multiple populations (MPs) with distinctive light element abundances is a widespread phenomenon in clusters older than 6 Gyr. Clusters with masses, luminosities, and sizes comparable to those of ancient globulars are still forming today. Nonetheless, the presence of light element variations has been poorly investigated in such young systems, even if the knowledge of the age at which this phenomenon develops is crucial for theoretical models on MPs. We use J-band integrated spectra of three young (7-40 Myr) clusters in NGC 4038 to look for Al variations indicative of MPs. Assuming that the large majority (>70%) of stars are characterised by high Al content - as observed in Galactic clusters with comparable mass; we find that none of the studied clusters show significant Al variations. Small Al spreads have been measured in all the six young clusters observed in the near-infrared. While it is unlikely that young clusters only show low Al whereas old ones display different levels of Al variations; this suggests the possibility that MPs are not present at such young ages at least among the high-mass stellar component. Alternatively, the fraction of stars with field-like chemistry could be extremely large, mimicking low Al abundances in the integrated spectrum. Finally, since the near-infrared stellar continuum of young clusters is almost entirely due to luminous red supergiants, we can also speculate that MPs only manifest themselves in low mass stars due to some evolutionary mechanism.