Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1982
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1982aj.....87..203k&link_type=abstract
Astronomical Journal, vol. 87, Jan. 1982, p. 203-217.
Astronomy and Astrophysics
Astronomy
10
Astronomical Spectroscopy, Digital Data, Fast Fourier Transformations, Image Processing, Power Spectra, Spiral Galaxies, Astronomical Photography, Data Smoothing, Fourier Analysis, Galactic Structure, H Alpha Line, Image Filters, Mathematical Models, Spectral Bands, Spectrum Analysis, Ultraviolet Spectra
Scientific paper
Several digitized images of galaxies M83, MS 1, and NGC 1365 have been analyzed using two-dimensional Fast Fourier Transform techniques. Markedly different power spectra (i.e., the equivalent of optical diffractograms) are obtained depending on the galaxy chosen and the photometric band of the image. For M83, the Hα power spectrum reveals only long-range correlations characteristic of a distorted or segmented spiral shape. The power spectra of the ultraviolet and red spectral images, although different, show both long- and short-range order which would be present in well defined spiral arms. Using Fourier image-filtering techniques, it has also been possible to separate the size components in a galactic image. Low-pass filtering reveals the larger spatial frequencies of the fundamental spiral shapes, while high-pass filtering reveals small uncorrelated objects. A number of filtering experiments of this type have been performed. The second part of this study involves the Fourier analysis of computer-modeled ideal spirals with linear, logarithmic, and hyperbolic shapes as a function of radial distance. In order to approach the images of real galaxies, various modifications to these shapes have been evaluated. These modifications include: center smoothing, variable arm width, additive noise radial arm segmenting, and center feature reduction. The power spectrum of a hyperbolic model with the appropriate combination of these modifications most closely resembles that of M83 in the ultraviolet.
Huntley Jonathan M.
Krakow W.
Seiden Philip E.
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