Luminosity--Line-Width Relations and the Extragalactic Distance Scale. II. A Comparison with Types IA and II Supernovae

We present a comparison of galaxy distances estimated via the luminosity-line-width or Tully-Fisher relation and those estimated using supernovae. In the first case, we compare to distances estimated by assuming Type Ia supernovae (SNe Ia) are standard candles. The sample is restricted to those late-type galaxies which have had both reasonably well observed supernova events and which are also suitable for an application of the luminosity-line-width relation. Given this selection criteria, the resulting sample of 16 galaxies should be essentially free of "Malmquist-like" effects. Consequently, the observed dispersion between the two methods should only reflect that intrinsic in the two techniques and enable a fair assessment of the precision of the two methods. The Hubble diagram for the sample has an rms dispersion of only 0.4 mag, implying that both techniques are reasonably accurate indicators of extragalactic distances and have small intrinsic dispersion (~0.3 mag, or 15% in distance). The calibration of the luminosity-line-width relations obtained in Paper I using Cepheid and RR Lyrae variables provides an absolute calibration for SNe Ia of M_B_ = - 18.74 +/- 0.14. Existing data on more distant SNe Ia are used to derive a global estimate of the Hubble Constant, the result being H_0_ = 86 +/- 7 km s^-1^ Mpc^-1^. Alternatively, if we force H_0_ ~ 45 km s^-1^ Mpc^-1^, the luminosity- line-width relations would still have a small rms dispersion but must then have a discontinuous absolute calibration of {DELTA}m = 1.4 mag over a small range in distance, namely, 4.0 < D_TF_ < 6.5 Mpc. We also present a similar comparison using distances estimated via the method of modeling the expanding photospheres of Type II supernovae (SNe II). In this case, the mean distance ratio for 11 SNe II and their parent galaxies is D_TF_/D_SN II_ = 0.89 +/- 0.05, with an rms dispersion of only 11% in distance, or equivalently 0.22 mag. This implies that the SN II method is at least as reliable as assuming SNe Ia are standard candles, and that the luminosity-line-width relations produce accurate distance estimates as well (0.16 mag). That is, the distances estimated via these two methods are completely consistent within the stated internal errors. Consequently, discrepancies in the value of the Hubble Constant estimated using the SN II method and the TF relation are not significant.