Adsorption line Survey of H+3 in the Galactic Center: The Warm and Diffuse Gas in the Central Molecular Zone

H3是宇宙中最基本的分子离子。它在离子中性反应中具有很大的朗之万反应速率，在星际化学中起着举足轻重的作用。对于高温(50-500K)低密度(50-200 cm−-3)气体，H3的振动跃迁是唯一的探针，其他分子，如CO，是不敏感的。利用红外H3线，我们在银河系的中央分子带(CMZ)发现了一个巨大的热扩散气体储藏库。气体的密度与银盘中的扩散云相似，但温度要高得多(~250K)。CMZ云的填充因子明显大于0.1，成为银河系中心新的主要介质群。在云层中，H2的宇宙射线电离率比银盘的任何其他部分至少高一个数量级(ζ&gt；10−15 S−1)。高ζ对银河系中心的能量学具有潜在的重要意义，因为它可以解释气体的动能如何有效地转化为热能。在这个节目中，我们将在银河系大规模演化的背景下，调查云的物理范围、CMZ内部的温度和密度分布，并最终探讨云的起源。

H+3 is the most fundamental molecular ion in the universe. It plays a pivotal role in the interstellar chemistry for its large Langevin reaction rate in ion-neutral reactions. The vibrational transition of H+3 is a unique probe for high-temperature (50–500 K) low-density (50–200 cm−3) gas, that other molecules, for instance CO, are not sensitive. Using infrared H+3 lines, we have found a large reservoir of warm and diffuse gas in the Central Molecular Zone (CMZ) of our Galaxy. The gas has similar density with the diffuse clouds in the Galactic disk, but the temperature is much higher (~250K). The filling factor of the cloud in the CMZ is significantly larger than 0.1, which makes it a new major population of the medium in the Galactic center. The cosmic ray ionization rate of H2 is at least one order of magnitude higher (ζ >10−15 s−1) in the cloud than in any other part of the Galactic disk. High ζ is potentially important for the energetics of the Galactic center, as it may explain how the kinetic energy of gas is efficiently converted to the thermal energy. In this program, we will investigate the physical extent of the clouds, the temperature and density profile inside the CMZ, and eventually the origin of the cloud in the context of the large-scale evolution of the Milky Way Galaxy.