The HI line width/linear diameter relationship as an independent test of the Hubble constant

The relationship between corrected H I line widths and linear diameters (LW/LD) for spiral galaxies is used as an independent check on the value of the Hubble constant. After calibrating the Tully-Fisher (TF) relation in both the B and I bands, the B-band relation is used for galaxies of morphological/luminosity types Sc I, Sc I.2, Sc I.3, Sab, Sb, Sb I-II, and Sb II to derive the LW/LD relation. We find that for this sample the scatter in the LW/LD is smallest with a Hubble constant of 90-95 km s(-1) Mpc(-1). Lower values of the Hubble constant produce a separation in the LW/LD relation that is a function of morphological type. Since a Hubble constant of 90-95 is significantly larger than the final Key Project value of 72 km s(-1) Mpc(-1), a comparison of TF, surface brightness fluctuation (SBF), and fundamental plane (FP) is made. This comparison indicates that the Key Project TF distances to 21 clusters may be too large. For a sample of 11 clusters, the Key Project TF distances provide an unweighted mean Hubble constant of 77 km s(-1) Mpc(-1), while a combination of the FP, SBF, and our TF distances for the same 11 clusters gives H-0=91 km s(-1) Mpc(-1). A more subtle result in our data is a morphological dichotomy in the Hubble constant. The data suggest that Sc I galaxies follow a Hubble constant of 90-95 while Sb galaxies follow a Hubble constant closer to 75 km s(-1) Mpc(-1). Possible explanations for this result are considered, but it is shown that this Sb/Sc I Hubble flow discrepancy is also present in the Virgo Cluster and is consistent with previous investigations that indicate that some galaxies carry a component of age-related intrinsic redshift.