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K. W. Willett (Lowell Observatory), B. G. Elmegreen (IBM T.J. Watson Research Center), D. A. Hunter (Lowell Observatory)
Fourier transform power spectra of major axis cuts in V and H\alpha images were made for a sample of 9 irregular galaxies. These power spectra reveal structure over a wide range of scales. For 6 of the galaxies the power spectrum slopes at intermediate scales (10--400 pc) range from -1.3 to -1.5. This is slightly shallower than what is observed elsewhere in H\,{\sc i}, molecular emission, dust extinction, and optical light. Three of the galaxies have flat power spectra like noise from the sky; these three galaxies are also relatively indistinct in the direct images. The power spectrum slope for H\alpha steepens with increasing star formation rate, ranging from a shallow value comparable to the noise at low rates to a steep value with a slope of ~1.5 at high rates. This change reflects the increasing areal filling factor of H\alpha emission with increasing star formation rate, and an apparently universal slope inside the H\alpha regions that is comparable to that for Kolmogorov turbulence. The power spectrum of H\,{\sc i} in one galaxy has a steeper power law, with a slope of ~2.9.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.