The 200-pc Molecular Cylinder in the Galactic Centre
  Analyzing the 3D structure of the molecular gas distribution in the central
200 pc region of the Galaxy, we show that the expanding molecular ring (EMR,
also known as the parallelogram) and the central molecular zone (CMZ) exhibit
quite different distributions and kinematics. The EMR composes a bipolar
vertical cylinder with the total length as long as $\sim 170$ pc and shows
large non-circular velocities. On the contrary, the CMZ is distributed in a
nearly rigid-body rotating ring and arms tightly concentrated near the galactic
plane with full thickness less than $\sim 30$ pc. Furthermore, the mass and
density ratios of the EMR to CMZ are as small as $\sim 0.13$ and $0.04$,
respectively. We discuss the origins of the EMR and CMZ based on the bar and
explosion models. We suggest that the EMR's large vertical extent can be
explained by a cylindrical shock wave model driven by an explosive activity in
the Galactic Centre.
