# The 200-pc Molecular Cylinder in the Galactic Centre

## TL;DR

This study reveals distinct 3D structures and kinematics of the molecular gas in the Galactic Centre, identifying the EMR as a bipolar cylinder and the CMZ as a rotating ring, and discusses their origins.

## Contribution

It provides a detailed 3D structural and kinematic analysis of the EMR and CMZ, proposing a shock wave model for the EMR's vertical extent.

## Key findings

- EMR is a bipolar vertical cylinder with ~170 pc length.
- CMZ is a nearly rigid-body rotating ring with <30 pc thickness.
- Mass and density ratios of EMR to CMZ are ~0.13 and 0.04.

## Abstract

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.