银河II中央0.5pc的恒星星族：初始质量函数
Stellar Populations in the Central 0.5 pc of the Galaxy II: The Initial Mass Function
摘要：
银河系中心的超大质量黑洞是一个巨大的年轻星系团的宿主，它可能是在银河系中最不适宜居住的环境中形成的。我们提出了新的测量这个集群的全局属性，包括初始质量函数（IMF），年龄和集群质量。这些结果是基于凯克激光导星自适应光学观测，用于识别年轻恒星并测量其KP波段光度函数，如Do等人2013所述。一个贝叶斯推断方法的发展，同时适合全球性的集群利用观测和广泛的模拟合成星团。我们发现这个星系团的质量函数的斜率为α= 1.7 +/- 0.2，比以前报道的要陡，但仍然比传统的Salpeter斜率2.35要平坦。该集群的年龄在250万至580万年之间，置信度为95%，这比通常采用的年龄要小，但在过去测量的不确定性范围内是一致的。星团的确切年龄是很难确定的，因为我们的结果显示了两个不同的年龄解决方案（3.9百万年和2.8百万年），由于模型退化的相对数量的沃尔夫-拉叶星和OB星。星团的总质量在14，000 - 37，000 \msun之间，大于1 \msun，为了拟合观测到的光度函数和观测到的沃尔夫-拉叶星的数量，需要包括多个恒星系统。新的IMF斜率测量现在与X射线观测相一致，表明与Salpeter IMF相比，发射X射线的前主序星比预期少10倍。银河系中心的年轻星系团是IMF的少数几个明确例子之一，它与太阳附近发现的接近普遍的IMF有很大的偏离。
英文摘要：
The supermassive black hole at the center of the Milky Way plays host to a massive, young cluster that may have formed in one of the most inhospitable environments in the Galaxy. We present new measurements of the global properties of this cluster, including the initial mass function (IMF), age, and cluster mass. These results are based on Keck laser-guide-star adaptive optics observations used to identify the young stars and measure their Kp-band luminosity function as presented in Do et al. 2013. A Bayesian inference methodology is developed to simultaneously fit the global properties of the cluster utilizing the observations and extensive simulations of synthetic star clusters. We find that the slope of the mass function for this cluster is α= 1.7 +/- 0.2, which is steeper than previously reported, but still flatter than the traditional Salpeter slope of 2.35. The age of the cluster is between 2.5-5.8 Myr with 95% confidence, which is a younger age than typically adopted but consistent within the uncertainties of past measurements. The exact age of the cluster is difficult to determine since our results show two distinct age solutions (3.9 Myr and 2.8 Myr) due to model degeneracies in the relative number of Wolf-Rayet and OB stars. The total cluster mass is between 14,000 - 37,000 \msun above 1 \msun and it is necessary to include multiple star systems in order to fit the observed luminosity function and the number of observed Wolf-Rayet stars. The new IMF slope measurement is now consistent with X-ray observations indicating a factor of 10 fewer X-ray emitting pre-main-sequence stars than expected when compared with a Salpeter IMF. The young cluster at the Galactic center is one of the few definitive examples of an IMF that deviates significantly from the near-universal IMFs found in the solar neighborhood.
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