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Optical tracers of spiral wave resonances in galaxies. II - Hidden three-arm spirals in a sample of 18 galaxies
Elmegreen, Bruce G.; Elmegreen, Debra M.; Montenegro, Luis
AA(IBM Thomas J. Watson Research Center, Yorktown Heights, NY), AB(Vassar College Observatory, Poughkeepsie, NY), AC(City College, New York)
Astrophysical Journal Supplement Series (ISSN 0067-0049), vol. 79, March 1992, p. 37-48. Research supported by Vassar College. (ApJS Homepage)
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NASA/STI Keywords:
Galactic Structure, Image Processing, Resonance, Spiral Galaxies, Interacting Galaxies, Irregular Galaxies, Star Formation, Wave Reflection
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An improved algorithm for extracting various types of symmetries from galaxy images is introduced. It preserves the nonlinear shapes of the spiral arms without introducing false interarm components, and it displays the m = 2, 3, 4, etc. subcomponents in whole galaxies all at once to avoid confusion with localized star formation and foreground stars. The algorithm is applied to 18 galaxies with various types of spirals. Conventional Fourier transform techniques are also used to study the arm structures. Underlying three-arm spirals are found to be common in the present sample, and a few galaxies have a complex four- or five-arm system, too. To check whether this structure is sensible, the termination radii of the two-, three-, and four-arm spirals are compared to the corresponding resonance radii predicted from theory. The symmetric components in nearly all of the galaxies are found to end at their outer wave-epicycle resonances.

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