Physical Conditions of Molecular Gas in the Galactic Center

Abstract

Abstract We estimated the physical conditions of molecular gas in the central molecular zone (CMZ) of the Galaxy, using our CO $J = 3-2$ data obtained with the Atacama Submillimeter Telescope Experiment (ASTE) in conjunction with J = 1–0 $^{12}$CO and $^{13}$CO data previously observed with the Nobeyama Radio Observatory (NRO) 45 m telescope. The large velocity gradient (LVG) approximation was employed. The distributions of gas density, kinetic temperature, and CO column density were derived as functions of the position and the velocity for the entire coverage of the CO $J = 3-2$ data. We fairly determined the physical conditions for 69% of data points in the CMZ with $\geq 1 \hskip2pt\sigma$ CO detections. The kinetic temperature was found to be roughly uniform in the CMZ, while the gas density was higher in the 120 pc star-forming ring than in the outer dust lanes. The physical conditions of high $J = 3-2/J = 1-0$ features are also discussed.