Compact ammonia sources toward the G10.5 + 0.0 H II region complex

Abstract

We present observations of the (2, 2) and (3, 3) inversion transitions of ammonia toward a group of compact H II regions near l = 10-degrees.5, b = 0-degrees.0, made at 4'' resolution using the VLA. We detected three distinct ammonia sources in a region of approximately 2' in diameter. The densest and hottest cloud, having a line center velocity of 66.9 +/- 0.2 km s-1, is associated with the G 10.47 + 0.03 cluster of ultracompact H II regions. It exhibits a core-halo structure, with a core of approximately 0.08 pc in size surrounded by an envelope of approximately 0.25 pc in diameter. The peak optical depth in the main line of the (2, 2) and (3, 3) transitions are 25 and 37, respectively. The rotational temperature of the ammonia gas rises from -25 K in the outer parts of the halo to -75 K at the center of the core. The ammonia column density rises from approximately 4 x 10(17) cm-2 in the envelope region to approximately 4 x 10(18) cm-2 in the central position. The NH3 emission from the core region is remarkably broad in velocity; the line widths of the (2, 2) and (3, 3) main lines are 12.2 +/- 1.2 and 11.6 +/- 0.5 km s-1, respectively. The observed velocity structure of the ammonia emission indicates that the halo is slowly rotating, with an angular velocity of 9.5 +/- 1.1 km s-1 pc-1, while the gas in the core is undergoing rapid motions. A second cloud, having an angular size of approximately 13', a line center velocity of 71.3 +/- 0.2 km s-1, and a line width of 3.5 km s-1, is found toward the G10.46 + 0.03 complex region of ionized gas. It has a rotational temperature of 48 +/- 6 K and an NH3 column density of approximately 1 X 10(16) cm-2. The velocity structure of the ammonia emission suggests that this cloud is probably expanding, with a velocity of approximately 2 km s-1. The third cloud, at l = 10-degrees-48, b = 0.03-degrees, has a size of approximately 9'', a line center velocity of 65.4 +/- 0.9 km s-1, and a line width of 3.5 km s-1, and is not associated with any known radio continuum emission. It may represent a molecular core undergoing gravitational collapse in a stage prior to the formation of a star.