用AAOmega测试牛顿引力：47 Tuc和M55的质-光分布和金属度校准
Testing Newtonian Gravity with AAOmega: Mass-To-Light Profiles and Metallicity Calibrations From 47 Tuc and M55
摘要：
球状星团是弱加速度下牛顿引力理论的重要实验平台，它对我们理解引力相互作用的本质至关重要。最近有人声称，球状星团的速度色散剖面在大半径处变平，尽管在这样的天体中明显缺乏暗物质，这表明需要修改引力理论。我们继续调查这一说法，获得了有史以来最大的光谱样本47 Tuccenda和M55。此外，这个大样本允许基于钙三重线的等效宽度和红巨星分支尖端的K带幅度进行精确的金属丰度校准。假设一个等温分布，每个集群的旋转也被测量与两个集群表现出明确的旋转签名。本文还计算了小麦哲伦云中的两个球状星团NGC 121和Kron 3的整体速度色散。通过对47 Tuc和M55的速度色散分布应用一个简单的动力学模型，我们计算了它们的质光分布、总质量和中心速度色散。我们发现没有统计上显着的扁平化的速度分散在大半径的M55，和一个显着的增加，在47 Tuc的半径大于约一半的潮汐半径的配置文件。我们将这种增加解释为蒸发特征，表明47 Tuc正在经历或已经经历核心坍缩，但在任何一个星团中都不需要暗物质或修改引力理论。
英文摘要：
Globular clusters are an important test bed for Newtonian gravity in the weak-acceleration regime, which is vital to our understanding of the nature of the gravitational interaction. Recent claims have been made that the velocity dispersion profiles of globular clusters flatten out at large radii, despite an apparent paucity of dark matter in such objects, indicating the need for a modification of gravitational theories. We continue our investigation of this claim, with the largest spectral samples ever obtained of 47 Tucanae and M55. Furthermore, this large sample allows for an accurate metallicity calibration based on the equivalent widths of the calcium triplet lines and K band magnitude of the Tip of the Red Giant Branch. Assuming an isothermal distribution, the rotations of each cluster are also measured with both clusters exhibiting clear rotation signatures. The global velocity dispersions of NGC 121 and Kron 3, two globular clusters in the Small Magellanic Cloud, are also calculated. By applying a simple dynamical model to the velocity dispersion profiles of 47 Tuc and M55, we calculate their mass-to-light profiles, total masses and central velocity dispersions. We find no statistically significant flattening of the velocity dispersion at large radii for M55, and a marked increase in the profile of 47 Tuc for radii greater than approximately half the tidal radius. We interpret this increase as an evaporation signature, indicating that 47 Tuc is undergoing, or has undergone, core-collapse, but find no requirement for dark matter or a modification of gravitational theories in either cluster.
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