  A correlation between (1) the difference between the Tully-Fisher calculated
distance and Cepheid calculated distance for a target galaxy and (2) the
magnitude and distance of galaxies close to the target galaxy is described. The
result is based on a sample of 31 galaxies that have published Cepheid
distances with a wide range of characteristics and distances from 2.02 Mpc to
49.7 Mpc. The energy impinging on a target galaxy from neighboring galaxies is
related to the residual between Tully-Fisher and Cepheid distance calculations
of the target galaxy. These relations have four different zones dependent on
the value of the impinging energy. The correlation coefficients are 0.77, 0.87,
0.81, and 0.98, respectively. This relationship is of interest not only for its
ability to reduce the Tully-Fisher to Cepheid distance residual but also
because it suggests neighboring galaxies have a strong influence on the
apparent luminosity of galaxies and it suggests the Tully-Fisher relationship
assumption that the intrinsic mass to intrinsic luminosity ratio is constant
among galaxies is valid for z < 0.006.
