Global Cosmological Parameters Measured Using Classical Double Radio Sources

Abstract

Fourteen classical double radio galaxies with redshifts between zero and two were used to determine the cosmological parameters ${\Omega }_m$, ${\Omega }_{\Lambda }$, and ${\Omega }_k$, where these are the normalized values of the mean mass density, cosmological constant, and space curvature at the present epoch. A low value of ${\Omega }_m$ is obtained, and ${\Omega }_m=1$ is ruled out with 97.5% confidence. The low value of ${\Omega }_m$ determined using the radio source method described here is also indicated by several independent tests. Thus, it appears that either a cosmological constant, or space curvature, is significant at the present epoch. This means that the universe is undergoing, or has recently undergone, a transition away from a state of matter domination and into a state where either a cosmological constant or space curvature is determining the expansion rate of the universe. The low value of ${\Omega }_m$ presented here and by Guerra & Daly (1998) means that we can state with 97.5 % confidence that the universe will continue to expand forever.

To appear in "Fundamental Parameters in Cosmology", The proceedings of the XXXIIIrd Rencontres de Moriond, eds. J. Trân Thanh Vân & Y. Giraud-Heraud, (Paris, France: Editions Frontieres)