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arXiv 1806.02580astro-ph.GA
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由盖亚DR2揭示的球状星团的内旋

The internal rotation of globular clusters revealed by Gaia DR2

P. Bianchini, R. P. van der Marel, A. del Pino, L. L. Watkins, A. Bellini, M. A. Fardal, M. Libralato, A. Sills

摘要:

视线运动学的研究表明,许多银河系球状星团有一个显着程度的内部旋转。然而,需要结合自行和视线速度的三维运动学来揭示角动量在这些古老恒星系统形成和演化中的作用。在这里,我们提出了第一个定量研究的内部旋转的平面上的天空大样本的球状星团使用自行盖亚DR 2。我们在$>$ 3-sigma置信水平下检测了51个集群中11个集群的自行切向分量中的旋转特征,证实了Gaia collaboration et al.(2018)中报告的8个集群的检测,并通过2-sigma旋转检测识别了11个GC。对于检测到的全局旋转的集群,我们构建的二维旋转地图和适当的运动旋转曲线,我们评估旋转相对于随机运动($V/σ\sim0.08-0.51$)的相关性。我们发现证据的内部旋转和弛豫时间的程度之间的相关性,突出了长期的动态演化的重要性,在塑造集群当前的属性。这有力地表明,角动量在团簇形成的早期阶段一定发挥了重要作用。最后,利用旋转地图的空间信息和视线数据的比较,我们提供了一个子集的8个集群的旋转轴的倾斜度的估计。我们的工作表明盖亚数据的球状星团的内部运动学研究的潜力,并提供了第一步,重建其内在的三维结构。

英文摘要:

Line-of-sight kinematic studies indicate that many Galactic globular clusters have a significant degree of internal rotation. However, three-dimensional kinematics from a combination of proper motions and line-of-sight velocities are needed to unveil the role of angular momentum in the formation and evolution of these old stellar systems. Here we present the first quantitative study of internal rotation on the plane-of-the-sky for a large sample of globular clusters using proper motions from Gaia DR2. We detect signatures of rotation in the tangential component of proper motions for 11 out of 51 clusters at a $>$3-sigma confidence level, confirming the detection reported in Gaia collaboration et al. (2018) for 8 clusters, and additionally identify 11 GCs with a 2-sigma rotation detection. For the clusters with a detected global rotation, we construct the two-dimensional rotation maps and proper motion rotation curves, and we assess the relevance of rotation with respect to random motions ($V/σ\sim0.08-0.51$). We find evidence of a correlation between the degree of internal rotation and relaxation time, highlighting the importance of long-term dynamical evolution in shaping the clusters current properties. This is a strong indication that angular momentum must have played a fundamental role in the earliest phases of cluster formation. Finally, exploiting the spatial information of the rotation maps and a comparison with line-of-sight data, we provide an estimate of the inclination of the rotation axis for a subset of 8 clusters. Our work demonstrates the potential of Gaia data for internal kinematic studies of globular clusters and provides the first step to reconstruct their intrinsic three-dimensional structure.

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