Hot Molecular Gas in the Galactic Center

Using the new 23 GHz receivers at the Very Large Array (VLA), we have detected NH3(6,6) emission (ν = 25.056025 GHz) from hot (> 150 K) molecular clouds in the central 10 pc of the Galaxy. This is the first successful detection of NH3(6,6) with the VLA. The brightest emission comes from a region interior to the “circumnuclear disk” (CND), less than 1.5 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) and (3,3) emission as well as NH3(6,6) line widths have peak values within 1.5 pc of Sgr A*, indicating that the gas is physically close to the nucleus. NH3(6,6) is also detected towards many features outside the CND observed in NH3(1,1), (2,2), and (3,3). These features tend to lie along ridges of gas associated with Sgr A East or the massive “molecular ridge” that connects the “20 km s−1” and “50 km s−1” giant molecular clouds (GMCs). Subject headings: Galaxy: center — ISM: clouds — ISM: molecules — radio lines: ISM