Astron. Astrophys. 331, 709-725 (1998)

Sub-arcsecond structure of hot cores in the NH₃ (4,4) line ^*

R. Cesaroni ¹, P. Hofner ², C.M. Walmsley ¹ and E. Churchwell <sup>3

1</sup> Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy
² Cornell University, Arecibo Observatory, P.O. Box 995, Arecibo, Puerto Rico 00613
³ Washburn Observatory, University of Wisconsin-Madison, 475 North-Charter Street, Madison, WI 53706, USA

Received 5 August 1997 / Accepted 26 September 1997

Abstract

We present high angular resolution (, corresponding roughly to 0.015 pc) VLA observations in the ammonia (4,4) inversion transition of 3 hot cores associated with UC HII regions (G10.47+0.03, G29.96-0.02, G31.41+0.31), We have for the first time resolved the emission from these structures and present maps of the integrated intensity and optical depth. The main findings of this work are the existence of velocity and temperature gradients in the cores, suggesting that they are rotating disk-like structures with temperature decreasing with increasing distance R from the centre as . In G10.47+0.03, the blue-shifted absorption seen towards three embedded UC HII regions is used to derive their position along the line of sight. Finally, the evolutionary status and the star formation efficiency of the three cores is discussed, and we conclude that at least in the case of G10.47+0.03 the Miller & Scalo (1979) Initial Mass Function is inappropriate to describe the stellar content of the core. Also, we suggest that early type stars tend to form from filaments of dense molecular gas which fragment along their axis.

Key words: ISM: clouds Hii regions ISM: individual objects: G10.47+0.03, G29.96-0.02, G31.41+0.31 ISM: molecules radio lines: interstellar

* Based on data collected at the NRAO Very Large Array. The National Radio Astronomy Observatory is operated by Associated Universities, Inc., under cooperative agreement with the National Science Foundation.

Send offprint requests to: R. Cesaroni

© European Southern Observatory (ESO) 1998

Online publication: February 16, 1998
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