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Optical Thickness of the Galactic Absorption Layer and Its Ratio of Total to Selective Absorption

Published online by Cambridge University Press:  08 February 2017

Heinz Neckel
Heinz Neckel*
Affiliation:
Hamburg Observatory, Hamburg, Germany

Extract

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As is Well Known, the surface brightness within the galaxies decreases strongly with increasing distance from the center. Therefore, if the diameters of the galaxies are defined by the isophote of a distinct apparent surface brightness, these diameters become smaller and smaller with increasing galactic absorption. The diameters are defined in reference 1 in this manner (by the isophote 26ṃ15/sec2); therefore, the mean surface brightnesses derived in that reference correspond more and more to the inner, brighter parts of the galaxies as the absorption increases. Consequently, in the derivation of the half optical thickness a of the galactic absorption layer from the variation of the mean surface brightnesses S of 113 spiral galaxies with galactic latitude β, the assumption in reference 1, dS/d(csc β) = a, is not correct but has to be replaced by the more complicated formula

Type
Research Article
Information
International Astronomical Union Colloquium , Volume 7: Proper Motions , August 1965 , pp. 39 - 43
Copyright
Copyright © Kluwer Academic Publishers 1965

References

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