The Extragalactic Distance Scale

Abstract

Cepheid variables are used to derive a Virgo cluster distance of 16.0 +/- 1.5 Mpc. In conjunction with the Coma velocity and the well-established Coma/Virgo distance ratio, this yields a Hubble paprameter Ho = 81 +/- 8 km/s/Mpc. By combining this value with an age of the Universe of at least 16.8 +/- 2.1 Gyr, that is derived from the metal-poor globular cluster M92, one obtains f(Omega,Lambda) > 1.39 +/- 0.22. This value is only marginally consisitent with an Einstein-de Sitter universe with Omega=0 and Lambda=0, which has f=1. An Einstein-de Sitter universe with Omega=1 and Lambda=0, for which f=2/3, appears to be excluded at the 3-sigma level. It is shown that some small recent values of Ho resulted from the intrinsic dispersion in the linear diameters of galaxies, and from the fact that well-observed supernovae of Type Ia exhibit a luminosity range of ~20 at maximum light.