| Abstract | The IR 21 cm linewidth-absolute magnitude relation is calibrated by means of local galaxies with known distances, including new distance determinations of M33 and M81. The calibrated relation is applied to 17 Virgo cluster galaxies of type Sab to Sd and yields a cluster modulus of (m-M)0Virgo = 31.47+/-0.34. Reliable relative distance indicators are used to extend the distance scale to the Coma cluster, for which a distance modulus is found of (m-M)0Coma = 35.39+/-0.35. The blue 21 cm linewidth-absolute magnitude relation gives slightly larger distances. A combination of the two methods leads to a Hubble constant at the distance of the Coma cluster of H0=55+/-9 km s-1 Mpc-1. This value agrees with the global value of H0 = 50+/-7 km s-1 Mpc-1, giving a Hubble time of Ho-1 = 19.5×103 Myr, in aggreement with the age of the chemical elements and with the age of our Galaxy, determined from globular clusters. |
