Distances to Galaxies from the Correlation Between Luminosities and Linewidths. III. Cluster Template and Global Measurements of H0

Abstract

The correlation between the luminosities and rotation velocities of galaxies can be used to estimate distances to late-type galaxies. It is an appropriate moment to re-evaluate this method given the great deal of new information available. The major improvements described here include: (a) the template relations can now be defined by large, complete samples, (b) the samples are drawn from a wide range of environments, (c) the relations are defined by photometric information at B,R,I and K' bands, (d) the multi-band information clarifies problems associated with internal reddening, (e) the template zero-points are defined by 24 galaxies with accurately known distances, and (f) the relations are applied to 12 clusters scattered across the sky and out to velocities of 8,000 km/s. The biggest change from earlier calibrations are associated with point (e). Roughly a 15% increase in the distance scale has come about with the five-fold increase in the number of zero-point calibrators. The overall increase in the distance scale from the luminosity--linewidth methodology is about 10% after consideration of all factors. Modulo an assumed distance to the Large Magellanic Cloud of 50 kpc and no metallicity corrections to the Cepheid calibration, the resulting value of the Hubble Constant is H0 = 77 +- 8 km/s/Mpc where the error is the 95% probable statistical error. Cummulative systematic errors internal to this analysis should not exceed 10%. Uncertainties in the distance scale ladder external to this analysis are estimated at 10%. If the Cepheid calibration is shifted from the LMC to NGC 4258 with a distance established by observations of circum-nuclear masers then H0 is larger by 12%.