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Comparison of turbulence in HII regions and molecular clouds

Published online by Cambridge University Press:  03 August 2017

C. R. O'Dell
C. R. O'Dell*
Affiliation:
Department of Space Physics and Astronomy Rice University P. O. Box 1892 Houston, Texas, 77251 USA

Abstract

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Both the HII Regions and the Molecular Clouds show broadening of their emission lines beyond that expected from thermal motion and this is ascribed to turbulence. Turbulence in molecular clouds generally agrees with a model where the velocity of motion is determined by the Alfv én velocity.

Turbulence in Galactic HII Regions and Giant Extragalactic HII Regions can also be studied by the width of the emission lines. The magnitude of the turbulent velocities in these regions are characteristically about 10 km/s. There is a general increase in turbulent velocity with the size of the HII Region, and this relation is close to but different from the one third power dependence expected from the most naive application of Kolmogorov theory. When a detailed study is conducted of each Galactic HII Region by means of the structure function, one finds that there is not agreement with Kolmogorov theory.

The Size-Turbulent versus Velocity relation for Galactic HII Regions differs slightly from the better defined velocity relation for Giant Extragalactic HII Regions. This difference is probably due to the fact that the larger extragalactic objects are probably complexes of multiple individual HII Regions. There is no evidence that broadening of extragalactic HII Regions is due to motion about a common center of mass.

Type
Poster Sessions
Information
Symposium - International Astronomical Union , Volume 147: Fragmentation of Molecular Clouds and Star Formation , 1991 , pp. 476 - 479
Copyright
Copyright © Kluwer 1991 

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