Physical Contact between the +20 km/s Cloud and the Galactic Circumnuclear Disk

TL;DR

This study presents evidence of a physical contact and possible collision between the +20 km/s molecular cloud and the Galactic circumnuclear disk, suggesting a mechanism for mass transfer in the central Galaxy region.

Contribution

It introduces new observational evidence and interpretation of a collision between the +20 km/s cloud and the CND, highlighting a potential process for mass accretion.

Findings

Detection of an emission bridge connecting the cloud and the CND

Chemical analysis suggests the bridge's properties are intermediate between the two objects

Collision may facilitate mass transfer into the CND

Abstract

This paper reports the discovery of evidence for physical contact between the Galactic circumnuclear disk (CND) and an exterior giant molecular cloud. The central 10 pc of our Galaxy has been imaged in the HCN J=1-0, HCO+ J=1-0, CS J=2-1, H13CN J=1-0, SiO J=2-1, SO N_J=2_3-1_2, and HC3N J=11-10 lines using the Nobeyama Radio Observatory 45 m radio telescope. Based on our examination of the position-velocity maps of several high-density probe lines, we have found that an emission "bridge" may be connecting the +20 km/s cloud (M-0.13-0.08) and the negative-longitude extension of the CND. Analyses of line intensity ratios imply that the chemical property of the bridge is located between the +20 km/s cloud and the CND. We introduce a new interpretation that a part of the CND may be colliding with the 20 km/s cloud and the collision may be responsible for the formation of the bridge. Such collisional events could promote mass accretion onto the CND or into the inner ionized cavity, which may be further tested by proper motion studies.