For multicomponent spiral disks, the authors derive a relation for individual stellar components between the total surface density of mass and the observed luminosity scale height and vertical velocity dispersion. A criterion is given for the validity of the relation in the presence of spheroidal mass distributions and an inhomogeneous disk. Mass models for the Milky Way and NGC 891, 4565, and 5907 are used to illustrate what velocity dispersions observers might expect to measure in nearly face-on spiral galaxies.
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Bahcall et al. (1984) studied this question.