M31中的星团：V.内部动力学趋势：有些麻烦，有些令人放心
Star Clusters in M31: V. Internal Dynamical Trends: Some Troublesome, Some Reassuring
摘要：
我们目前的内部速度色散和精确的径向速度为200球状星团（GC）在M31中，来自使用新的高分辨率光谱MMT/Hectochelle。其中，163个还具有King模型结构参数，使我们能够估计它们的质光比。到目前为止，这是包括银河系在内的任何星系的最大的此类数据集。这些数据有力地证实了早期的建议，即M31 GC的光学和近红外质光比随着金属丰度的增加而下降。这种行为与标准初始质量函数的恒星星族模型所预测的相反。我们表明，这种现象似乎并没有引起标准的动力学演化。对于富含金属的GC，一个较浅的质量函数（dN/dM ~ M^-0.8 ~ M^-1.3，低于1个太阳质量）可以解释大部分现存的观测结果。我们还观察到一个一致的，单调的质光比和集群质量之间的相关性。这种相关性，与金属丰度的相关性相比，很好地解释了公认的模型的动力学演化的GC通过质量分离和低质量恒星的优先损失，这些数据是最好的约束这一过程。
英文摘要：
We present internal velocity dispersions and precise radial velocities for 200 globular clusters (GCs) in M31 that are derived using new high-resolution spectra from MMT/Hectochelle. Of these, 163 also have King model structural parameters that allow us to estimate their mass-to-light ratios. This is, by far, the largest such dataset available for any galaxy, including the Milky Way. These data strongly confirm earlier suggestions that the optical and near-infrared mass-to-light ratios of M31 GCs decline with increasing metallicity. This behavior is the opposite of that predicted by stellar population models for a standard initial mass function. We show that this phenomenon does not appear to be caused by standard dynamical evolution. A shallower mass function for metal-rich GCs (with dN/dM ~ M^-0.8 to M^-1.3 below one solar mass) can explain the bulk of extant observations. We also observe a consistent, monotonic correlation between mass-to-light ratio and cluster mass. This correlation, in contrast to the correlation with metallicity, is well-explained by the accepted model of dynamical evolution of GCs through mass segregation and the preferential loss of low-mass stars, and these data are among the best available to constrain this process.
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