Do spiral galaxies have a variable disk thickness

In this paper, the author discusses a model that describes the disk thickness, Δ, of spiral galaxies. Previous fits of the variable disk thickness using Δ(r) = b + cexp(ar), result in c > 0, thus giving an increase of Δ with r. The mean error of c, however, was so large that such effects could not be considered as statistically significant. Here the author gives theoretical arguments that causes to accept c > 0 as a viable result. For that purpose he expounds the consequences of a variable disk thickness on the vertical velocity dispersion. Two models of the velocity dispersion are compared in a table: the Spitzer-Schwarzschild mechanism; and a mechanism using general perturbation of the surface mass density. (Auth.)