The connecting molecular ridge in the Galactic center

TL;DR

This study uses high-resolution molecular line observations to identify a new connecting ridge structure in the Galactic center, revealing its connection to the disk and providing insights into gas dynamics and vertical lifting mechanisms.

Contribution

It reports the discovery of the connecting ridge in the Galactic center, linking the polar arc to the disk with detailed molecular line data and analysis.

Findings

The connecting ridge is connected to the disk in both spatial and velocity domains.

High CS line ratios indicate high excitation conditions in the structure.

The structure's detection was enabled by high excitation and low surface brightness sensitivity.

Abstract

We report new observations of multiple transitions of the CS molecular lines in the SgrA region of the Galactic center, at an angular resolution of 40" (=1.5 pc). The objective of this paper is to study the polar arc, which is a molecular ridge near the SgrA region, with apparent non-coplanar motions, and a velocity gradient perpendicular to the Galactic plane. With our high resolution dense-gas maps, we search for the base and the origin of the polar arc, which is expected to be embedded in the Galactic disk. We find that the polar arc is connected to a continuous structure from one of the disk ring/arm in both the spatial and velocity domains. This structure near SgrA* has high CS(J=4-3)/CS(J=2-1) ratios >1. That this structure has eluded detection in previous observations, is likely due to the combination of high excitation and low surface brightness temperature. We call this new structure the connecting ridge. We discuss the possible mechanism to form this structure and to lift the gas above the Galactic plane.