Constraints on mass loss and self-enrichment scenarios for the globular clusters of the Fornax dSph
Constraints on mass loss and self-enrichment scenarios for the globular clusters of the Fornax dSph
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DOI：
10.1051/0004-6361/201219897
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发表时间：
2012-07
影响因子：
6.5
通讯作者：
S. Larsen;J. Strader;J. P. F. R. U. Nijmegen;The Netherlands.;Harvard-Smithsonian Cfa;Usa;M. University;UCOLick Observatory
中科院分区：
文献类型：
--
作者：
S. Larsen;J. Strader;J. P. F. R. U. Nijmegen;The Netherlands.;Harvard-Smithsonian Cfa;Usa;M. University;UCOLick Observatory
最近，高色散光谱已经证明了在天炉座矮球状星系中的五个球状星团（GC）中有四个是非常贫金属的，[Fe/H]<− 2。剩下的星团，天炉座4，[Fe/H]=-1.4。这与场星的金属丰度分布形成鲜明对比，场星的金属丰度分布在[Fe/H] − 1附近有一个宽峰，只有少数恒星的[Fe/H]<− 2。如果我们只考虑[Fe/H]<− 2的恒星和星团，我们会发现一个极高的GC比频率，SN = 400，这意味着迄今为止已知的GC与场星的最高比率。我们估计，在天炉座dSph中[Fe/H]<− 2的所有恒星中，约有1/5 - 1/4属于四个最贫金属的GC。因此，这些GC最初最多可能是4 - 5倍大。然而，天炉座GC似乎与银河系GC具有相同的异常化学丰度模式，通常归因于星系团内存在多个恒星世代。在天炉座dSph中，贫金属GC星与场星的极端比例很难与GC的自富集和早期演化相协调，其中大部分（90%-95%）的第一代恒星已经丢失。它还表明，GC可能没有形成一个更大的人口的一部分，现在中断集群与初始的幂律质量分布。天炉座dSph可能是制约星星团的形成、自增强和早期动力学演化理论的罗塞塔石。
Recently, high-dispersion spectroscopy has demonstrated conclusively that four of the five globular clusters (GCs) in the Fornax dwarf spheroidal galaxy are very metal-poor with [Fe/H]<−2. The remaining cluster, Fornax 4, has [Fe/H] =−1.4. This is in stark contrast to the field star metallicity distribution which sh ows a broad peak around [Fe/H]≈ −1 with only a few percent of the stars having [Fe/H]<−2. If we only consider stars and clusters with [Fe/H]<−2 we thus find an extremely high GC specific frequency, SN ≈ 400, implying by far the highest ratio of GCs to field stars kno wn anywhere. We estimate that about 1/5‐1/4 of all stars in the Fornax dSph with [Fe/H]<−2 belong to the four most metal-poor GCs. These GCs could, therefore, at most have been a factor of 4‐5 more massive initially. Yet, the Fornax GCs appear to share the same anomalous chemical abundance patterns known from Milky Way GCs, commonly attributed to the presence of multiple stellar generations within the clusters. The extreme ratio of metal-poor GC- versus field stars in the Fornax dSph is di ffi cult to reconcile with scenarios for self-enrichment and ea rly evolution of GCs in which a large fraction (90%‐95%) of the first-generation sta rs have been lost. It also suggests that the GCs may not have formed as part of a larger population of now disrupted clusters with an initial power-law mass distribution. The Fornax dSph may be a rosetta stone for constraining theories of the formation, self-enr ichment and early dynamical evolution of star clusters.