Phase Interchange of Galactic Interstellar Gas Explored by the Terahertz Heterodyne Sensing

在这项研究中，我们主要研究了星际气体在银河系中的相交换，并进行了以下两个方面的研究。一是利用超导HEB混合器研制了太赫兹外差接收器，以探索氮离子谱线(1.46太赫兹)的分布。利用这条线，我们可以研究等离子体气体在分子云形成和演化中的作用。利用Nobeama射电观测站的设备，我们制作了一种扩散冷却HeB混频元件，其微桥结构为Nb，尺寸为100 nm。经过多次试验，我们最终确定了采用提升法的制造工艺。将混频元件安装在波导型混频模块上进行射频测试，并确认混频工作在800 GHz。尽管仍有一些问题需要克服，但我们已经为实现太赫兹天文HEB混频接收器奠定了坚实的基础。在上述发展研究的基础上，我们利用富士山亚毫米波望远镜观测原子碳的精细结构线，研究了分子云的形成和演化。特别是，我们观察到了明亮的边缘球体，它们受到附近OB恒星的强烈紫外线辐射的照射。在一个年轻的明亮的边缘球体IC1396中，我们发现原子碳的分布遍及整个云层，而不是集中在明亮的边缘。另一方面，在一个相当古老的球体λori中，我们在明亮的边缘位置发现了原子碳发射的峰值。这表明，随着云团的演化，原子碳逐渐转变为CO，并且只存在于OB星照射下的PDR层。因此，我们进一步证实了原子碳可以作为研究分子云形成和演化的良好示踪剂。

In this study, we focused on the phase interchange of interstellar gas in the Galaxy, and conducted the following two researches.The first one is a development of the THz heterodyne receiver using the superconductive HEB mixer in order to explore the distribution of the nitrogen ion line (1.46THz). With this line, we can study a role of plasma gas in formation and evolution of molecular clouds. By using the facilities at Nobeyama Radio Observatory, we have fabricated a diffusion cooled HEB mixer element which has a microbridge structure of Nb with a size of a few 100nm. After many trials, we finally established the fabrication process using the liftoff method. The mixer element was mounted on the waveguide mixer block for the RF test, and we have confirmed the mixer operation at 800GHz. Although we have still some problems to overcome, we were able to form a strong base toward realizing the HEB mixer receiver for the THz astronomy.Along with the above development study, we studied formation and evolution of molecular clouds by observing the fine structure line of the atomic carbon with the Mount Fuji submillimeter-wave telescope. Particularly, we observed bright rimmed globules, which are illuminated by strong UV radiation from a nearby OB stars. In a young bright rimmed globule, IC1396, we found that the distribution of the atomic carbon extends over the entire of the clouds, not concentrating at the bright rim. On the other hand, we found a peak of the atomic carbon emission at the bright rim position in a rather old globule, λ Ori. This indicates that the atomic carbon gradually changes into CO as the cloud evolves, and that it only exists in the PDR layer illuminated by OB stars. Therefore we further confirmed that the atomic carbon can be a good tracer to study formation and evolution of molecular clouds.