Dynamical masses and mass-to-light ratios of resolved massive star clusters – II. Results for 26 star clusters in the Magellanic Clouds
Dynamical masses and mass-to-light ratios of resolved massive star clusters – II. Results for 26 star clusters in the Magellanic Clouds
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DOI：
10.1093/mnras/stab1065
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发表时间：
2021-04
期刊：
影响因子：
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通讯作者：
Ying-Yi Song;M. Mateo;J. Bailey;M. Walker;I. Roederer;E. Olszewski;M. Reiter;A. Kremin
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文献类型：
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作者：
Ying-Yi Song;M. Mateo;J. Bailey;M. Walker;I. Roederer;E. Olszewski;M. Reiter;A. Kremin
我们提供了26个麦哲伦云（MC）星团中单个恒星的光谱，目的是在年龄和金属丰度的广泛范围内估计动态质量和v波段质量光比（M/LV）。我们在麦哲伦/克莱望远镜上使用M2FS获得了3137个高分辨率的恒星光谱。结合239个已发表的质量相当的光谱结果，我们最终得到了2787颗具有高质量光谱的恒星样本，用于目标星团的运动学分析。从这些光谱中测量的视距速度和每个星团内的恒星位置被用于定制的期望最大化（EM）技术来估计星团成员概率。利用适当的集群结构参数和相应的单质量动力学模型，该技术最终提供了每个集群的自一致的总质量和M/LV估计。还获得了簇的平均金属丰度，并将其与基于钙IR三重金属物的尺度联系起来。我们提出了星团的M/LV值随星团年龄、质量和金属丰度的变化趋势，并发现我们的结果比一组简单恒星群（SSP）模型的预测平均低约40%。考虑内部和外部动态效应的修正SSP模型大大提高了与我们的结果的一致性，采用强底光IMF的模型也是如此。在动态演变必须发生的情况下，不需要修改后的IMF来匹配数据和模型。相比之下，我们的聚类样本排除了底部重的IMF，因为这将导致更高的预测M/LV值，显著增加与我们观察结果的差异。
We present spectroscopy of individual stars in 26 Magellanic Cloud (MC) star clusters with the aim of estimating dynamical masses and V-band mass-to-light (M/LV ) ratios over a wide range in age and metallicity. We obtained 3137 high-resolution stellar spectra with M2FS on the Magellan/Clay Telescope. Combined with 239 published spectroscopic results of comparable quality, we produced a final sample of 2787 stars with good quality spectra for kinematic analysis in the target clusters. Line-of-sight velocities measured from these spectra and stellar positions within each cluster were used in a customized expectation-maximization (EM) technique to estimate cluster membership probabilities. Using appropriate cluster structural parameters and corresponding single-mass dynamical models, this technique ultimately provides self-consistent total mass and M/LV estimates for each cluster. Mean metallicities for the clusters were also obtained and tied to a scale based on calcium IR triplet metallicites. We present trends of the cluster M/LV values with cluster age, mass and metallicity, and find that our results run about 40 per cent on average lower than the predictions of a set of simple stellar population (SSP) models. Modified SSP models that account for internal and external dynamical effects greatly improve agreement with our results, as can models that adopt a strongly bottom-light IMF. To the extent that dynamical evolution must occur, a modified IMF is not required to match data and models. In contrast, a bottom-heavy IMF is ruled out for our cluster sample as this would lead to higher predicted M/LV values, significantly increasing the discrepancy with our observations.