An Observational Study of Expanding Gas Shell in the Galaxy and the Magellanic Clouds

本研究旨在揭示星系演化过程中恒星形成的物理过程，重点研究超壳层可能发挥的作用。我们采用的方法是对本星系群、银河系和大小麦哲伦星云三个星系的分子云和恒星形成进行了详细的研究。我们揭示了分子云在银河系尺度上的演化方案的前所未有的细节，并得出结论，与包括随机湍流压缩在内的其他过程相比，超壳层的作用并不占主导地位。在这项研究的过程中，我们首先证明了大麦哲伦星云是三个星系中最可靠的，因为其他两个有意义的样本数量要少得多，大约只有20-30个，这是由于污染或恒星形成不太活跃。另一方面，大麦哲伦星云有近200个样本，可以与大质量恒星形成的迹象进行重要的比较。我们利用其他地方的HII区域和年轻星团的观测数据来识别单个分子云中的大质量恒星形成，揭示了三种类型的分子云，(1)无恒星，(2)只有HII区域，(3)有星团和富含HII区域。这三个类别很可能代表了演化序列，而大星云中的完整统计数据使我们第一次能够估计单个星系的整个演化时间尺度。这些结果在国际社会中得到了高度评价，在过去的国际会议上，包括2005年的原恒星和行星V会议上，多次邀请讨论这个问题。

This research aimed at revealing the physical process of star formation in galactic evolution with an emphasis on the possible role of supershells. The method we employed was to make a detailed study of molecular clouds and star formation in the three galaxies of the Local group, the Milky Way, and the Large and Small Magellanic Clouds. We have revealed unprecedented details of the evolutionary scheme of molecular clouds on a galactic scale and conclude that the role of supershells is not dominant as compared with the other processes including stochastic turbulent compression.In the course of this research, we first showed that the Large Magellanic Cloud is the most reliable galaxy among the three, because the other two have much smaller number of samples with significance, around only 20-30, due to the contamination or the less active star formation. The Large Magellanic Cloud on the other hand has nearly 200 samples that allowed to make significant comparison with signs of massive star formation. We used observational data on HII regions and young star clusters taken elsewhere to identify massive star formation in the individual molecular clouds to reveal the three classes of molecular clouds, (1)starless, (2)with HII regions only and (3)with clusters and rich HII regions. These three classes likely represent the evolutionary sequence and the complete statistics in the Large Cloud allowed us to estimate the whole evolutionary timescale for the first time in a single galaxy.These results are highly evaluated in the international community and several invited talks were given on the subject in the past international meetings including Protostars and Planet V in 2005.