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

• Final Report Year: 2015

Final Report Abstract

H3+ is the most fundamental molecular ion in the Universe. It plays a pivotal role in the interstellar chemistry for its large Langevin rate in ion-neutral reactions. The vibrational transition of H3+ is a unique probe of high-temperature (50–500 K) low-density (50–200 cm^−3 ) molecular medium that is hard to detect by other molecular probes such as CO. Using infrared H3+ lines, we found a large reservoir of warm and diffuse gas in the Central Molecular Zone of our Galaxy. The gas has similar density with the diffuse clouds outside the Galactic center, but the temperature is much higher (∼250 K). The filling factor of the cloud in the CMZ is significantly larger than 1/10. The cosmic ray ionization rate of H2 is at least one order of magnitude higher (ζ2 >10^−15 s^−1 ) in the cloud than in any other part of the Galactic disk. High ζ2 is potentially important for the energetics of the Galactic center, as it may explain how the macroscopic mechanical energy of the clouds in the Galactic center can be converted to the thermal energy of the gas. In this program, we will investigated the physical extent of the clouds, the temperature and density profile inside the CMZ with the eventual goal to uncover the origin of the warm and diffuse cloud in the context of the large-scale evolution of the Milky Way.

Publications

• “Fundamental vibrational transitions of hydrogen chloride detected in CRL 2136” A&A, 558, L5 (2013)
  Goto, M., Usuda, T., Geballe, T. R., Menten, K. M., Indriolo, N., Neufeld, D. A.
  
• “H3+ Spectroscopy and the Ionization Rate of Molecular Hydrogen in the Central Few Parsecs of the Galaxy”, Journal of Physical Chemistry, A. 117, 9919 (2013)
  Goto, M., Indriolo, N., Geballe, T. R., Usuda, T.
  
• “Infrared H3+ and CO Studies of the Galactic Core: GCIRS 3 and GCIRS 1W”, ApJ, 786, 96 (2014)
  Goto, M., Geballe, T. R., Indriolo, N., Yusef-Zadeh, F., Usuda, T., Henning, Th., Oka, T.
  
• “Infrared absorption toward NGC 7538 IRS 1, H2 , H3+, and CO”, ApJ (2015)
  Goto, M., Geballe, T. R., Usuda, T.