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37. Galactic radio emission and the distribution of discrete sources: Introductory Lecture

Published online by Cambridge University Press:  14 August 2015

R. Hanbury Brown
R. Hanbury Brown*
Affiliation:
Jodrell Bank Experimental Station, University of Manchester, England

Extract

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At wave-lengths greater than about 1 metre the majority of the radio emission which is observed from the Galaxy cannot be explained in terms of thermal emission from ionized interstellar gas. This conclusion is widely accepted and is based on observations of the equivalent temperature of the sky and the spectrum of the radiation. The spectrum at metre wave-lengths is of the general form: where TA is the equivalent black-body temperature of a region of sky and λ is the wave-length. The exponent n varies with direction but lies between about 2·5 and 2·8, and is thus significantly greater than the value of 2·0 which is the maximum to be expected for thermal emission from an ionized gas. Furthermore, the value of TA is about 1050K. at 15 metres and thus greatly exceeds the electron temperature expected in H 11 regions.

At centimetre wave-lengths it is likely that the majority of the radiation observed originates in thermal emission from ionized gas; however, the present discussion is limited to a range of wave-lengths from about 1 to 10 metres where the ionized gas in the Galaxy is believed to be substantially transparent and where the origin of most of the radiation is believed to be non-thermal.

Type
Part III: Galactic Structure and Statistical Studies of Point Sources
Information
Symposium - International Astronomical Union , Volume 4: Radio Astronomy , 1957 , pp. 211 - 217
Copyright
Copyright © Cambridge University Press 1957 

References

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