Hot Molecular Gas in the Central 10 Parsecs of the Galaxy

Robeson McGary Herrnstein1 & Paul T.P. Ho1

1 Harvard-Smithsonian CfA

E-mail contact:

See ApJ, 559, 326 (2001)

The metastable (J=K) rotation inversion transitions of NH3 are known to be good tracers of the warm, dense material near the Galactic Center. We present maps of the central 10 parsecs of the Galaxy in NH3(1,1), (2,2), (3,3), and (6,6) made with the Very Large Array (VLA). These are the first successful observations of NH3(6,6) ( GHz) with the VLA, made possible by a recent upgrade of the 23 GHz receivers. The full velocity coverage and spatial sampling of these maps enables the detection of many new filamentary streamers in the central 10 pc. NH3 emission shows a high correlation with thermal dust emission and is not highly affected by absorption. Molecular ridges of emission are found along the northern, eastern, and western edges of the expanding shell, Sgr A East, indicating that this feature plays an important role in the molecular environment near the Galactic Center. At 412 K above ground, NH3(6,6) gives us a rare opportunity to study the hottest molecular gas in the region. The brightest NH3(6,6) emission comes from a region interior to the ``circumnuclear disk'' (CND), less than ~2 pc in projected distance from Sgr A*. This region does not show molecular emission from lower energy transitions such as NH3(1,1) and (2,2), HCN(1-0) and HCO+(1-0). Line ratios of NH3(6,6) to (3,3) emission as well as NH3(6,6) line widths have peak values within 1 pc of Sgr A*, indicating that the gas may be physically close to the nucleus. In addition, a highly heated extension of the ``southern streamer'' towards Sgr A* is observed, supporting the idea that the streamer is approaching the nucleus.