Paper: astro-ph/0601078
Date: Wed, 4 Jan 2006 13:43:02 GMT (659kb)

Title: Ammonia in Infrared Dark Clouds

Authors: Thushara Pillai (1), Friedrich Wyrowski (1), Sean J. Carey (2), Karl
M. Menten (1) ((1)Max-Planck-Institut fuer Radioastronomie, Bonn (2)Spitzer
Science Center, California Institute of Technology)

Comments: 17 pages, 11 figures, in press in Astronomy & Astrophysics
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Infrared Dark Clouds appear to be the long sought population of cold and
dense aggregations with the potential of harbouring the earliest stages of
massive star formation. Up to now there has been no systematic study on the
temperature distribution, velocity fields, chemical and physical state toward
this new cloud population. Knowing these properties is crucial for
understanding the presence, absence and the very potential of star formation.
The present paper aims at addressing these questions. We analyse temperature
structures and velocity fields and gain information on their chemical
evolution. The gas emission is remarkably coextensive with the extinction seen
at infrared wavelengths and with the submillimeter dust emission. Our results
show that IRDCs are on average cold (T < 20 K) and have variations among the
different cores. IRDC cores are in virial equilibrium, are massive (M > 100
M_sun), highly turbulent (1 -- 3 km/s) and exhibit significant velocity
structure (variations around 1 -- 2 km/s over the cloud). We find an increasing
trend in temperature from IRDCs with high ammonia column density to high mass
protostellar objects and hot core/Ultracompact Hii regions stages of early warm
high-mass star formation while linewidths of IRDCs are smaller. On the basis of
this sample, we infer that while active star formation is not yet pervasive in
most IRDCs, local condensations might collapse in the future or have already
begun forming stars.

\\ ( http://arXiv.org/abs/astro-ph/0601078 , 659kb)