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Direct measurement of the optical depth in a spiral galaxy

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An Erratum to this article was published on 15 October 1992

Abstract

FROM a statistical analysis of nearly 9,400 spiral galaxies1, Valentijn2 has claimed that the disks of spirals are largely opaque. His argument derives from a lack of inclination dependence in the average surface brightness of the spirals, which if they were transparent would be brighter when seen edge-on than face-on. This statistically derived result is however vulnerable to several selection effects3, and seems to contradict the fact that the survey was successfully performed (as we live in a transparent spiral galaxy) as well as anecdotal examples of galaxies visible through other galaxies. We have tried to measure directly optical extinction in a number of spiral disks, using pairs in which a foreground spiral is backlit by another galaxy. In our best example substantial extinction of starlight occurs, but the extinction is mostly associated with the spiral features in which much of the light arises in the first place. This correlation of extinction with emission may account for both the transparency and apparent opacity of spiral galaxies.

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References

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Authors and Affiliations

  1. Department of Physics and Astronomy, University of Alabama, Box 870324, Tuscaloosa, Alabama, 35487-0324, USA

    Raymond E. White III & William C. Keel

Authors
  1. Raymond E. White III
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  2. William C. Keel
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White, R., Keel, W. Direct measurement of the optical depth in a spiral galaxy. Nature 359, 129–131 (1992). https://doi.org/10.1038/359129a0

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  • DOI: https://doi.org/10.1038/359129a0

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