GALAXY COLORS IN DISTANT CLUSTERS AS A TEST FOR THE WORLD MODEL

Colors of elliptical galaxies in nine distant clusters (z less-than-or -equal-to 0.5) are studied with reference to theoretical models for ev olutionary population synthesis (Buzzoni 1989) inferring allowed range s for the relevant cosmological parameters. Galaxies at z = 0.2 are fo und to be coeval within +/- 3 Gyr and consistent with an absolute age of 12 Gyr. The look-back time from z = 0.2 to z = 0.45 is not larger t han 4 Gyr. In a Fiedmann cosmology this leads to a current age of the universe of 16 +/- 2 Gyr and an upper limit to the Hubble constant of 68 km s-1 Mpc-1. The value of H0 = 52 +/- 2 recently suggested by Sand age and Tammann is supported by the data. In this case the deceleratio n parameter is found to be q0 = 0.06(-0.06)+0.14. We also find margina l evidence for galaxies to form at redshift z(f) > 5. The Einstein-de Sitter model is not supported by observations if LAMBDA0 = 0 unless we accept an exceedingly low value for H-0 less-than-or-equal-to 41 km s -1 Mpc-1. A zero-curvature space would rather demand lambda0 > 0.35 [l ambda0 = 1/3LAMBDA0(c/H0)2]] with a preferred range 0.6 less-than-or-e qual-to lambda0 less-than-or-equal-to 0.85. Accordingly, the density p arameter OMEGA0 should range between 0.15 and 0.4 with an upper limit about 0.65.