The ASTE Galactic Center CO J=3-2 Survey: Probing Shocked Molecular Gas
  in the CMZ
  Large-scale CO surveys have revealed that the central molecular zone (CMZ) of
our Galaxy is characterized by a number of expanding shells/arcs, and by a
peculiar population of compact clouds with large velocity widths --
high-velocity compact clouds (HVCCs). We have performed a large-scale CO J=3-2
survey of the CMZ from 2005 to 2008 with the Atacama Submillimeter-wave
Telescope Experiment (ASTE). The data cover almost the full extent of the CMZ
and the Clump 2 with a 34 arcsec grid spacing. The CO J=3-2 data were compared
with the CO J=1--0 data taken with the Nobeyama Radio Observatory 45 m
telescope. Molecular gas in the CMZ exhibits higher J=3-2/J=1-0 intensity
ratios [R(3-2/1-0)=0.7] than that in the Galactic disk [R(3-2/1-0)=0.4]. We
extracted highly excited, optically thin gas by the criterion, R(3-2/1-0)>=1.5.
Clumps of high R(3-2/1-0) gas were found in the Sgr A and Sgr C regions, near
SNR G 0.9+0.1, and three regions with energetic HVCCs; CO 1.27+0.01, CO
-0.41-0.23, and CO -1.21-0.12. We also found a number of small spots of high
R(3-2/1-0) gas over the CMZ. Many of these high R(3-2/1-0) clumps and spots
have large velocity widths, and some apparently coincides with HVCCs,
suggesting that they are spots of shocked molecular gas. Their origin should be
local explosive events, possibly supernova explosions. These suggest that the
energetic HVCCs are associated with massive compact clusters, which have been
formed by microbursts of star formation. Rough estimates of the energy flow
from large to small scale suggest that the supernova shocks can make a
significant contribution to turbulence activation and gas heating in the CMZ.
