The Global Hubble Constant

Abstract

A review of large-scale investigations of the determination of H is presented. The infrared period-luminosity relation of Cepheids gives distances accurate to -2% to nearby galaxies. Based on the distances of M31, MH, N300 and N2403, a DM of 31 ·30 ±O· 20 has been derived to the nearby Virgo cluster from the TF relation of spirals at four wavebands. Distances to more distant clusters extending up to a redshift of -10000 km S-I obtained through the CM relation of E galaxies, the TF relation of spirals and the velocity dispersion-luminosity relation of E galaxies give a value of H of 71 km S-I Mpcl when these distances are normalised to a Virgo DM of 31·30. The scatter in the redshift-distance relation of these clusters is -500 km s-I arising from the presence of unaccounted peculiar motions of individual clusters. The magnitude limited all-sky samples of galaxies also give a value of H near 70 km S-I Mpcl once the data are corrected for Malmquist bias. The best value of the global Hubble constant obtained from the redshift-distance data of Virgo and farther clusters, as well as the magnitude limited samples involving various methods of determining distances by different observers, is 73 km S-i Mpcl . Taking into account the error in the calibration of our DM of Virgo we can set a generous error of 10 to this value of H.