A search for scale-dependent morphology in five molecular cloud complexes

IRAS 100 micron intensity images and 60 micron optical depth maps of five molecular cloud complexes are analyzed using area-perimeter analysis. It is found that a noninteger Hausdorff dimension describes the shape of clouds and condensations within the complexes; that is, cloud areas are generally a noninteger power of perimeter, so that the projected two-dimensional shapes of these objects are fractal. The effect of noise on the cloud images is analyzed, and it is demonstrated that this result is not an artifact but reflects a fundamental irregularity of the clouds which probably arises from turbulence. The Hausdorff dimensions do not differ substantially from those found for terrestrial and interstellar cirrus clouds. No evidence of smooth morphology is found, implying that the correlation length of the turbulence driving the morphological irregularities within the clouds is less than 0.3 pc. Strong evidence of a measurable decline in Hausdorff dimension with decreasing scale is also found.