对47个图卡坦半岛的AAOmega观测：过去合并的证据？
AAOmega Observations of 47 Tucanae: Evidence for a Past Merger?
摘要：
球状星团47 Tuccenda被很好地研究过，但它有许多无法解释的特征，包括在大半径处速度色散剖面的显著上升，这表明两个不同的运动学种群的可能性。在这封信中，我们采用贝叶斯方法来分析最大的光谱数据集的47 Tuccenda，以确定这显然是两个组成部分的人口是真实的。假设在考虑数据之前，这两个模型的可能性相等，我们发现证据支持双组分总体模型的因子约为3x10^7。这一结果的几种可能的解释进行了探讨，即蒸发的低质量的恒星，一个分层合并，现存的残余物的两个最初分离的人口，和多个恒星形成的时代。我们发现对双分量速度分布最令人信服的解释是，47 Tuc形成为两个独立的群体，来自同一个原始星团云，合并<7.3 +/- 1.5 Gyr前。这也可以解释该星系团的极端旋转、低质光比和混合的恒星星族。
英文摘要：
The globular cluster 47 Tucanae is well studied but it has many characteristics that are unexplained, including a significant rise in the velocity dispersion profile at large radii, indicating the exciting possibility of two distinct kinematic populations. In this Letter we employ a Bayesian approach to the analysis of the largest available spectral dataset of 47 Tucanae to determine whether this apparently two-component population is real. Assuming the two models were equally likely before taking the data into account, we find that the evidence favours the two-component population model by a factor of ~3x10^7. Several possible explanations for this result are explored, namely the evaporation of low-mass stars, a hierarchical merger, extant remnants of two initially segregated populations, and multiple star formation epochs. We find the most compelling explanation for the two-component velocity distribution is that 47 Tuc formed as two separate populations arising from the same proto-cluster cloud which merged <7.3 +/- 1.5 Gyr ago. This may also explain the extreme rotation, low mass-to-light ratio and mixed stellar populations of this cluster.
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