NH3in the Central 10 pc of the Galaxy. I. General Morphology and Kinematic Connections between the Circumnuclear Disk and Giant Molecular Clouds

Abstract

New Very Large Array images of NH3 (1, 1), (2, 2), and (3, 3) emission in the central 10 pc of the Galaxy trace filamentary streams of gas, several of which appear to feed the circumnuclear disk (CND). The NH3 images have a spatial resolution of 165 × 145 and have better spatial sampling than previous NH3 observations. The images show the southern streamer, 50 km s-1 cloud, and new features including a western streamer, 6 pc in length, and a ridge, which connects to the CND. NH3 (3, 3) emission is very similar to 1.2 mm dust emission, indicating that NH3 traces column density well. Ratios of the NH3 (2, 2) to (1, 1) line intensities give an estimate of the temperature of the gas and indicate high temperatures close to the nucleus and CND. The new data cover a velocity range of 270 km s-1, including all velocities observed in the CND, with a resolution of 9.8 km s-1. Previous NH3 observations with higher resolution did not cover the entire range of velocities seen in the CND. The large-scale kinematics of the CND do not resemble a coherent ring or disk. We see evidence for a high-velocity cloud within a projected distance of 50'' (2 pc), which is only seen in NH3 (3, 3) and is likely to be hot. Comparison to 6 cm continuum emission reveals that much of the NH3 emission traces the outer edges of Sagitarrius A East and was probably pushed outward by this expanding shell. The connection between the northern ridge (which appears to be swept up by Sgr A East) and the CND indicates that Sgr A East and the CND are in close proximity to each other. Kinematic evidence for these connections is presented in this paper, while the full kinematic analysis of the central 10 pc will be presented in our next paper.