Abstract
In order to detect the gravitational effect of the dark corona component of disk galaxies, it is necessary to have surface photometry and rotation data that extend well beyond three disk-scale lengths. Such data exists now for several pure disk galaxies. There is very strong evidence for dark coronas in these galaxies. It has been possible to estimate the scale length and density for their dark components, which can be well represented as isothermal spheres. The pure disk galaxies that have been studied so far have absolute magnitudes in the range - 17 > M B > - 19.5. It would be very interesting to know whether the fainter dwarf irregular galaxies (which are also disk systems) have dark coronas: are these coronas necessary for disk galaxies to form?
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