The I–Band Tully–Fisher Relation and the Hubble Constant

The application of the I band Tully–Fisher relation towards determining the Hubble constant is reviewed, with particular attention to the impact of scatter and bias corrections in the relation. A template relation is derived from galaxies in 24 clusters. A subset of 14 clusters with cz ∼ 4000 to 9000 km s is used as an inertial frame to define the velocity zero point of the relation. Twelve galaxies with Cepheid distances are used to establish the absolute magnitude scale of the Tully–Fisher relation, and thus to determine a value of H◦ = 70 ± 5 km s −1 Mpc . Estimates of the peculiar velocities of the Virgo and Fornax clusters are also given. Assuming that the distance to Fornax is 18.2 Mpc (N1365), H◦ = 76± 8 km s −1 Mpc . Assuming that Virgo lies at 17.4 Mpc (M100, N4496, N4639), H◦ = 67± 8 km s −1 Mpc .