A new I-band Tully-Fisher relation for the Fornax Cluster: Implication for the Fornax distance and local supercluster velocity field

The Fornax Cluster represents an important step in the extragalactic distance scale. Here we present a new I-band luminosity-H I velocity width (I-band Tully-Fisher) study of the cluster using an enlarged sampled of spiral galaxies in Fornax. I-band CCD photometry and 21 cm parameters are measured for 23 members of Fornax and compared with data for the Virgo Cluster. We obtain an accurate distance modulus of Fornax relative to Virgo of -0.06 +/- 0.15 mag. The low scatter of Fornax galaxies around the Tully-Fisher relation will make the cluster an ideal calibrator once a direct measurement of its distance is obtained. Furthermore, the H I content of the galaxies does not seem affected by the cluster environment. Here we use two different absolute calibration methods which yield an absolute distance to Fornax of 15.4 +/- 2.3 Mpc (absolute distance modulus of 30.94 +/- 0.33 mag). A simple model yields a Local Group Virgocentric flow velocity of 224 +/- 90 km s(-1) which corresponds to a Hubble constant of H-o = 74 +/- 11 km s(-1) Mpc(-1) from the Fornax data.