A DIAMETER EFFECT IN THE TULLY-FISHER RELATION AND ITS CONSEQUENCES

The southern spiral galaxies data of Mathewson et al. are analysed. In the clusters the deviations from an inverse Tully-Fisher relation are correlated with deviations from a diameter-magnitude relation. This implies an additional parameter in the Tully-Fisher relation. When this diameter effect is taken into account, regions away from the general direction of the Great Attractor show a smooth Hubble flow out to at least V(CMB) = 8000 km s-1. The Mathewson et al. data in the general direction of the Great Attractor are consistent with either a net flow towards our Galaxy for objects at distances of about 8000 km s-1 or a quiet Hubble flow at this distance. Direct measurements of all the quantities required for a definitive application of the diameter term to the absolute calibration of the Tully-Fisher relation are not yet available. However, the use of the best current estimates of the quantities involved leads to a provisional estimate for the Hubble constant of H-0 = 5 3 km s-1 Mpc-1 rather than about 85 km s-1 Mpc-1, the value obtained when the diameter effect is neglected.