KINEMATICS OF THE LOCAL UNIVERSE. X. H0 FROM THE INVERSE B-BAND TULLY-FISHER RELATION USING DIAMETER AND MAGNITUDE LIMITED SAMPLES

We derive the value of H_0 using the inverse diameter and magnitude B-band Tully-Fisher relations and the large all-sky sample KLUN (5171 spiral galaxies). Our kinematical model was that of Peebles centered at Virgo. Our calibrator sample consisted of 15 field galaxies with cepheid distance moduli measured mostly with HST. A straightforward application of the inverse relation yielded H_0\approx 80 km/sec/Mpc for the diameter relation and H_0\approx 70 km/sec/Mpc for the magnitude relation. H_0 from diameters is about 50 percent and from magnitudes about 30 percent larger than the corresponding direct estimates (cf. Theureau et al. 1997b). This discrepancy could not be resolved in terms of a selection effect in log V_max nor by the dependence of the zero-point on the Hubble type. We showed that a new, calibrator selection bias (Teerikorpi et al. 1999), is present. By using samples of signicificant size (N=2142 for diameters and N=1713 for magnitudes) we found for a homogeneous distribution of galaxies (alpha=0) H_0\approx 50 km/sec/Mpc for both the diameters and magnitudes. Also H_0's from a fractal distribution of galaxies (decreasing radial number density gradient alpha=0.8) agree with the direct predictions. This is the first time when the inverse Tully-Fisher relation clearly lends credence to small values of the Hubble constant H_0 and to long cosmological distance scale consistently supported by Sandage and his collaborators.