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

在本研究中，我们重点研究了银河系星际气体的相交换，并进行了以下两项研究。第一个是利用超导HEB混频器开发太赫兹外差接收机，以探索氮离子线（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。利用野山射电天文台的设备，我们制作了一个扩散冷却HEB混合器元件，该元件具有几个100nm大小的Nb微桥结构。经过多次试验，我们最终确定了采用升空法的制造工艺。混频器元件被安装在波导混频器模块上进行射频测试，我们已经确认了在800GHz的混频器操作。虽然我们仍然有一些问题需要克服，但我们能够为实现HEB混合接收器的太赫兹天文学奠定坚实的基础。在进行上述发展研究的同时，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。特别地，我们观察到明亮的边缘球体，它们被附近OB星的强紫外线辐射照亮。在一个年轻的明亮边缘球体IC1396中，我们发现碳原子的分布延伸到整个云层，而不是集中在明亮的边缘。另一方面，我们在一个相当古老的球λ Ori的明亮边缘位置发现了原子碳发射的峰值。这表明碳原子随着云的演化逐渐转变为CO，并且它只存在于被OB星照亮的PDR层中。因此，我们进一步证实了碳原子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.