The Hubble Parameter
Abstract
Distance determinations to individual galaxies, groups, and clusters are critically reviewed. All modern distance determinations have been reduced to a common and internally consistent system. These distances are then used to discuss the present status of the extragalactic distance scale and of the Hubble Parameter, H_O. It is shown that the classical distance scale "problem" starts quite abruptly at D > 3 Mpc. It is emphasized that the reasons for this discrepancy are entirely independent of difficulties associated with large-scale deviations from a smooth Hubble flow. From eight different techniques the mean distance modulus of the Virgo cluster is found to be (m-M)_o = 31.0 +/- ).15 (D = 15.8 +/- 1.1 Mpc). Twelve determinations of the difference between the distance moduli of the Coma and Virgo clusters yield Delta(m-M)_o = 3.71 +/- 0.05 mag and hence a Coma distance modulus (m-M)_o = 34.71 +/- 0.16 (D = 87 +/- 6 Mpc). Combining this distance with the Coma cluster's cosmological velocity of 7210 km s^-1 yields a value H_o (local) = 83 +/- 6 km s^-1 Mpc^-1. From the velocity-distance relation for the brightest galaxies in clusters of Bautz-Morgan types I and I-II it is found that H_o (global)/H_o(local) = 0.92 +/- 0.08, in which "local" refers to northern clusters with V_o < 10,000 km s^-1. In other words the cluster data do not show a statistically significant difference between the local and global values of the Hubble parameter. If one nevertheless adopts H_o(global)/H_o(local) = 0.92 +/- 0.08 then one obtains H_o(global) = 76 +/- 9 km s^-1 Mpc^-1. This observed value of H_o differs at the 3 sigma level from that predicted by theories of stellar evolution in conjunction with canonical models of the Universe with Theta = 1 and Lambda = 0. (SECTION: Invited Review Paper)
- Publication:
-
Publications of the Astronomical Society of the Pacific
- Pub Date:
- October 1992
- DOI:
- 10.1086/133070
- Bibcode:
- 1992PASP..104..861V
- Keywords:
-
- Galactic Clusters;
- Hubble Constant;
- Local Group (Astronomy);
- Andromeda Galaxy;
- Distance;
- Dwarf Galaxies;
- Irregular Galaxies;
- Virgo Galactic Cluster;
- Astronomy;
- DISTANCE SCALE;
- INVITED REVIEW PAPER