VLA NH observations of regions of massive star formation in protostellar cores

¹ Astronomy Department and CAS-PKU Joint Beijing Astrophysics Center, Peking University, Beijing 100871, PR China e-mail: ywang@cfa.harvard.edu
² Harvard-Smithsonian Center for Astrophysics, Cambridge, MA 02138, USA
³ Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, PR China
⁴ I, Physics Institute, Koln Univ., Zulpicher St., 50937 Koln, Germany

Received: 1 January 2006
Accepted: 20 August 2006

Abstract

Aims.The high angular resolution images with the Very Large Array (VLA) allow us to explore the general properties of protostellar cores in massive star forming regions at large distances.

Methods.We observed the NH (J, K) = (1, 1) and (2, 2) lines toward five massive protostar candidates (IRAS 18196-1331, IRAS 18352-0148, IRAS 18361-0627, IRAS 18414-0339 and IRAS 19474+2637) with the VLA D configuration.

Results.We found that these objects have hundreds of solar masses in dense gas with rotation temperatures from 8 to 27 K. No 1.3 cm continuum emission was detected at an rms of ~0.7 mJy in all sources except IRAS 18361-0627. We identified 60 clumps and determined their physical parameters (e.g. line width, rotation temperature, size, and mass). The clump masses range from 0.1  to 4800 . The average size, line width and temperature are 0.1 ± 0.06 pc, 1.3 ± 0.4 km s^-1 and 16 ± 5 K. The discrepancy between NH and (sub)mm continuum emission is found in IRAS 18196-1331. This phenomenon could occur as a result of the NH abundance variation being affected by the UV illumination.