Takeshi Oka

PHYSICAL CONDITIONS OF MOLECULAR GAS IN THE GALAXY

Physical conditions of molecular gas are key parameters to the formation rate and initial mass function of stars formed in molecular clouds. The ongoing Tokyo-NRO survey has been observing the Galactic CO (J=2−1) emission with a beamsize matched to the Columbia CO (J=1−0) survey. Intensities of the two lines should reflect physical conditions of the COemitting gas. An out-of-plane survey of the inner Galaxy which covers from 20° to 60° in galactic longitude and from −1° to +l° in galactic latitude with grid spacings of 0.25° has already been made (Sakamoto et al. 1994). Its coverage is large enough to draw conclusions on global properties of molecular gas in the inner Galaxy.

A CO(J=2-1) line survey of the Galactic center

We have observed the Galactic center in 12CO(J= 2 - 1) and 13CO( J = 2 - 1) lines using the TokyoOnsala-ESO-Cal&n 60-cm telescope and compared the data with the 12CO(J= 1-O) Columbia survey (Bitran et al. 1997). The 12C0 J = 2- l/J = 1-O intensity ratio is very high (0.96) in the central 9OOpc of the Galaxy, although it is about 0.6-0.7 for typical molecular clouds in the Galactic disk. The observed intensity ratios, 12C0 J=2-l/J=l-0 and ‘3CO/‘2C0 (J=2-l), indicate that even the 12C0 line is not very optically thick: 71zco(k14) - 1 or smaller in the Galactic center. This may be due to high temperature and large velocity dispersion. The large velocity dispersion is probably caused by large external pressure and tidal forces. 01999 COSPAR. Published by Elsevier Science Ltd.

Gas in the CMZ toward the Galactic Nucleus Studied by H3 + and CO Spectra

Infrared spectroscopy of H3+ toward the Galactic center uncovered the presence of vast amount of diffuse (100 cm−3) and warm gas (250 K) filling the Central Molecular Zone of our Galaxy (CMZ; R 200 K) and moderately dense gas (200 cm−3) local in the Galactic nucleus. The absorption profiles of H3+ R(1,1)l consists of two components. The one is sharp absorption lines in the negative velocity, that represents the diffuse clouds in the foreground Galactic Arms. The other is the trough absorption spanning from −150 to +90 km s−1. The absorption profile of the trough component has detailed structure with several absorption minima, which was not noticed in the previous lower resolution ...

A large-scale CO imaging of the Galactic Center II. Dynamical properties of molecular clouds

Abstract The data from the Nobeyama Radio Observatory 45 m telescope Galactic Center CO survey have been analyzed to generate a compilation of molecular clouds with intense CO emission in this region. Clouds are identified in an automated manner throughout the main part of the survey data for all CO emission peaks exceeding 10 K ( T R ∗ ). Correlations between the size, velocity dispersion, virial mass, and the CO luminosity, for the molecular clouds in the Galactic center were shown. We diagnosed gravitational stabilities of identified clouds assuming that the disk clouds are nearly at the onset of gravitational instability. Most of the clouds and cloud complexes in the Galactic center are gravitationally stable, while some clouds with intense CO emission are gravitationally unstable.

A Large-Scale CO Imaging of the Galactic Center

Molecular gas in the Galactic center region is spatially and kinematically complex, and its physical conditions are distinctively different from those of molecular gas in the Galactic disk (e.g., Morris 1996). Relative paucity of current star formation activity, despite the abundance of dense molecular gas in this region, is one of the problem at issue.

Physical Conditions of Molecular Gas in the Galaxy

Physical conditions of molecular gas are key parameters to the formation rate and initial mass function of stars formed in molecular clouds. The ongoing Tokyo-NRO survey has been observing the Galactic CO (J=2-1) emission with a beamsize matched to the Columbia CO (J=1-0) survey. Intensities of the two lines should reflect physical conditions of the COemitting gas. An out-of-plane survey of the inner Galaxy which covers from 20° to 60° in galactic longitude and from -1° to + 1° in galactic latitude with grid spacings of 0.25° has already been made (Sakamoto et al. 1994). Its coverage is large enough to draw conclusions on global properties of molecular gas in the inner Galaxy.