Global cosmological parameters determined using classical double radio galaxies

A sample of 20 powerful extended radio galaxies with redshifts between zero and 2 were used to determine constraints on global cosmological parameters. Data for six radio sources were obtained from the VLA archive, analyzed, and combined with the sample of 14 radio galaxies used previously by Guerra & Daly to determine cosmological parameters. The new results are consistent with our previous results, and indicate that the current value of the mean mass density of the universe is significantly less than the critical value. A universe with Ω_m of unity in matter is ruled out at 99.0% confidence, and the best-fitting values of Ω_m in matter are 0.10^+0.25_-0.10 and -0.25^+0.35_-0.25 assuming zero space curvature and zero cosmological constant, respectively. Note that identical results obtain when the low-redshift bin, which includes Cygnus A, is excluded; these results are independent of whether the radio source Cygnus A is included. The method does not rely on a zero-redshift normalization. The radio properties of each source are also used to determine the density of the gas in the vicinity of the source, and the beam power of the source. The six new radio sources have physical characteristics similar to those found for the original 14 sources. The density of the gas around these radio sources is typical of gas in present-day clusters of galaxies. The beam powers are typically about 10⁴⁵ ergs s^-1.