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

• Applicant: Miwa Goto, Ph.D.
• Subject Area: Astrophysics and Astronomy
• Term: from 2011 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 203319529

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.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1573: Physics of the Interstellar Medium