Surface brightness fluctuations - A bridge from M31 to the Hubble constant

We present observations of the I-band surface brightness fluctuations of M32, M31, NGC 205, and 18 galaxies in the Fornax and Eridanus clusters. We confirm that MI_ has a very small scatter but find a substantially different calibration from earlier work based on theoretical isochrones. We attribute this to the isochrones underestimating the I-band bolometric corrections in very cool, luminous stars of solar metallicity. This new calibration puts M31 and M32 at the same distance which we take to be 0. 77 Mpc and gives us 5% distances to the galaxies in these other clusters. Our agreement with distances derived from the planetary nebula luminosity function confirms this estimate of precision. Using distances of clusters determined from the IR Tully-Fisher and Dₙ_-sigmar relations, which are tied to very distant galaxies and therefore measured in km s^-1^, we derive a value for the Hubble constant of 82 +/- 7 km s¹^ Mpc^-1^. We find, however, that while the IRTF results are remarkably consistent with the distances presented here, there is evidence of significant disagreement between Dₙ_-σ and these results.