A CO J = 3–2 Survey of the Galactic Center

Abstract

Abstract We have surveyed the central molecular zone (CMZ) of our Galaxy in the CO J$=$3–2 line with the Atacama Submillimeter-wave Telescope Experiment (ASTE). Molecular gas in the Galactic center shows a high J$= 3-2/J = 1-0$ intensity ratio ($\sim 0.9$), while gas in the spiral arms of the Galactic disk shows a lower ratio ($\sim 0.5$). The high-velocity compact cloud CO $0.02-0.02$ and the hyperenergetic shell CO 1.27$+$0.01, as well as gas in the Sgr A region, exhibit high J$=$3–2$/J=$1–0 intensity ratios exceeding 1.5. We also found a number of small spots of high-ratio gas. Some of these high-ratio spots have large velocity widths and some seem to be associated with nonthermal threads or filaments. These could be spots of hot molecular gas shocked by unidentified supernovae, which may be abundant in the CMZ.