  The rotation velocity asymmetry v observed in spiral galaxy HI rotation
curves linearly correlates with the effective potential force from the 10
closest neighboring galaxies normalized for the test particle mass and the
gravitational constant. The magnitude of the potential force from a close
galaxy is proportional to the luminosity of the close galaxy and inversely
proportional to the square of the distance from the close galaxy to the target
galaxy. The correlation coefficient is 0.99 and F test is 0.99. Also, the slope
of the rotation curve in the disk region of a galaxy from rising to flat to
declining is qualitatively correlated with increasing asymmetry and, hence, to
the net force from other galaxies. The result is based on a sample of nine
spiral galaxies with published Cepheid distances and rotation curves and with a
wide range of characteristics. These relationships are interesting not only for
their predictive power but also because (1) they suggest a galaxy's dynamics
and the shape of its rotation curve are related to the potential energy and
distance of neighboring galaxies, (2) they suggest a rising rotation curve in
the disk region is intrinsic, (3) they suggest the Tully-Fisher relationship's
assumption that the mass to intrinsic luminosity ratio is constant among
galaxies is valid, and (4) they are inconsistent with MOND, dark matter, and
the Linear Potential Model.
