(Proposal ID) S14A-106

(PI) Oka, Takeshi

(Proposal Title)
 Studies of the Central Molecular Zone of the Galactic Center by H3+ and CO

(Abstract)
The L band infrared spectrum of H_3^+ observed with the Subaru Telescope IRCS 
with its wide wavelength coverage is a novel unique probe to unravel mysteries 
of the Central Molecular Zone (CMZ), the central ~ 200 pc of the Galactic 
center (GC). Being a charged molecule with very simple chemistry, H_3^+ 
provides information that neutral molecules cannot provide, i. e., the 
ionization rate of the gas and hence the flux of low energy cosmic rays in 
the environment. Its rotational energy levels, custom made for studying warm 
and diffuse gas, allow us to determine temperature and density of the area 
reliably, and the rich velocity profiles of its absorption allow us to study 
morphology of the gas. In the last several years these studies have been 
drastically changing the previous concept of the gas in the center of 
astrophysical activities. We here propose to observe the H_3^+ spectrum toward 
newly found dust embedded stars to extend the region of studies. The 
observation of more stars will allow us to a better estimates of the volume 
filling factor of the newly found gas. It also helps to find more complete 
picture of the Expanding Molecular Ring (EMR) which our previous observations 
suggested. We also observe CO to discriminate gas in the CMZ and in the 
foreground.