NH 3 Observations of the Infrared Dark Cloud G28.34+0.06

Abstract

We present observations of the \nh3 (J,K) = (1,1) and (2,2) inversion transitions toward the infrared dark cloud G28.34+0.06, using the Very Large Array. Strong NH3 emission is found to coincide well with the infrared absorption feature in this cloud. The northern region of G28.34+0.06 is dominated by a compact clump (P2) with a high rotation temperature (29 K), large line width (4.3 km s$^{-1}$), and is associated with strong water maser (240 Jy) and a 24 $\mu$m point source with far IR luminosity of $10^3$ \lsun. We infer that P2 has embedded massive protostars although it lies in the 8 $\mu$m absorption region. The southern region has filamentary structures. The rotation temperature in the southern region decreases with the increase of the integrated NH3 intensity, which indicates an absence of strong internal heating in these clumps. In addition, the compact core P1 in the south has small line width (1.2 km s$^{-1}$) surrounded by extended emission with larger line width (1.8 km s$^{-1}$), which suggests a dissipation of turbulence in the dense part of the cloud. Thus, we suggest that P1 is at a much earlier evolutionary stage than P2, possibly at a stage that begins to form a cluster with massive stars.