Very Large Array Observations of Galactic Center OH 1720 MHz Masers in Sagittarius A East and in the Circumnuclear Disk

TL;DR

This study uses VLA radio observations to map 1720 MHz OH masers in the Galactic Center, revealing interactions between supernova remnants, molecular clouds, and the circumnuclear disk, and identifying new high-velocity masers.

Contribution

It provides detailed mapping of OH masers in the Galactic Center, clarifies their association with different structures, and introduces new high-velocity masers with insights into their excitation mechanisms.

Findings

Most masers are linked to Sgr A East interacting with molecular clouds.

New high-negative velocity masers support previous detections.

High velocity masers in the CND are likely pumped by internal dissipation, not shocks.

Abstract

We present Very Large Array (VLA) radio interferometry observations of the 1720 MHz OH masers in the Galactic Center (GC). Most 1720 MHz OH masers arise in regions where the supernova remnant Sgr A East is interacting with the interstellar medium. The majority of the newly found 1720 MHz OH masers are located to the northeast, independently indicating and confirming an area of shock interaction with the +50 km/s molecular cloud (M-0.02-0.07) on the far side of Sgr A East. The previously known bright masers in the southeast are suggested to be the result of the interaction between two supernova remnants, instead of between Sgr A East and the surrounding molecular clouds as generally found elsewhere in the Galaxy. Together with masers north of the circumnuclear disk (CND) they outline an interaction on the near side of Sgr A East. In contrast to the interaction between the +50 km/s cloud and Sgr A East, OH absorption data do not support a direct interaction between the CND material and Sgr A East. We also present three new high-negative velocity masers, supporting a previous single detection. The location and velocities of the high-negative and high-positive velocity masers are consistent with being near the tangent points of, and physically located in the CND. We argue that the high velocity masers in the CND are pumped by dissipation between density clumps in the CND instead of a shock generated by the supernova remnant. That is, the CND masers are not coupled to the supernova remnant and are sustained independently.