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Amazing Light pp 285-290 | Cite as

The Clumpy Structure of Molecular Clouds

  • Paul F. Goldsmith

Abstract

The structure of molecular clouds has been a puzzle since this dense phase of the interstellar medium was first recognized in the 1960’s. One of the very early indications of a “problem” with molecular cloud structure was the highly superthermal \( \left( {\delta \upsilon \gg \frac{{\sqrt {{kT}} }}{{{{m}_{{mol}}}}}} \right) \) and even supersonic \( \left( {\delta \upsilon > \frac{{\sqrt {{kT}} }}{{ < \mu > }}} \right) \)line widths found to characterize the emission from almost all types of molecular regions. This is very different, for example, from ionized HII regions, for which line widths reflect the temperature of the gas. The recognition that carbon monoxide and ammonia should be good molecular cloud thermometers [6, 32] allowed astronomers to establish that the temperature of these regions is between approximately 10 and 100 K [39,14]. The line widths observed in Giant Molecular Clouds (GMC’s) are typically an order of magnitude greater than the speed of sound in these regions. Only in the most quiescent cores of dark clouds (without embedded heating sources) does one find molecular line widths that are consistent with the gas temperature [2,11, 12, 22].

Keywords

Line Width Molecular Cloud Dark Cloud Giant Molecular Cloud Spontaneous Decay Rate 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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© Springer-Verlag New York, Inc. 1996

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  • Paul F. Goldsmith

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