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Optical HII regions

Published online by Cambridge University Press:  14 August 2015

Y. M. Georgelin ,
Y. P. Georgelin  and
J.-P. Sivan
Y. M. Georgelin
Affiliation:
Observatoire de Marseille and Laboratorie d'Astronomie Spatiale, Marseille, France
Y. P. Georgelin
Affiliation:
Observatoire de Marseille and Laboratorie d'Astronomie Spatiale, Marseille, France
J.-P. Sivan
Affiliation:
Observatoire de Marseille and Laboratorie d'Astronomie Spatiale, Marseille, France

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The ionized hydrogen regions seen on monochromatic Hα photographs of nearby spiral galaxies (e.g. Fig. 1) can be divided into four classes (Monnet, 1971): (1) bright, condensed, classical HII regions; (2) diffuse emission in the arms surrounding and connecting the classical regions (emission measure (EM) ∼ 150 cm−6 pc, for a gas electron temperature of 6000 K); (3) much fainter, diffuse emission extending over the entire disk (EM ∼ 50 cm−6 pc) in most Sc and Sd galaxies; (4) diffuse emission in the nuclear region.

Information

Type
II. THE DISK COMPONENT
Information
Symposium - International Astronomical Union , Volume 84: The Large-Scale Characteristics of the Galaxy , 1979 , pp. 65 - 72
Copyright
Copyright © Reidel 1979 

References

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