  We have made a conformal gravity fit to an available sample of 110 spiral
galaxies, and report here on the 20 of those galaxies whose rotation curve data
points extend the furthest from galactic centers. We identify the impact on the
20 galaxy data set of a universal de Sitter-like potential term $V(r)=-\kappa
c^2r^2/2$ that is induced by inhomogeneities in the cosmic background. This
quadratic term accompanies a universal linear potential term
$V(r)=\gamma_0c^2r/2$ that is associated with the cosmic background itself. We
find that when these two potential terms are taken in conjunction with the
contribution generated by the local luminous matter within the galaxies, the
conformal theory is able to account for the rotation curve systematics that is
observed in the entire 110 galaxy sample, without the need for any dark matter
whatsoever. With the two universal coefficients being found to be of global
magnitude, viz. $\kappa =9.54\times 10^{-54} {\rm cm}^{-2}$ and
$\gamma_0=3.06\times 10^{-30}{\rm cm}^{-1}$, our study suggests that invoking
the presence of dark matter may be nothing more than an attempt to describe
global effects in purely local galactic terms. With the quadratic potential
term having negative sign, galaxies are only able to support bound orbits up to
distances of order $\gamma_0/\kappa = 3.21\times 10^{23} {\rm cm}$, with global
physics thus imposing a natural limit on the size of galaxies.
