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 consisten t with our previous results, and indicate that the current value of the mea n mass density of the universe is significantly less than the critical valu e. A universe with Omega (m) of unity in matter is ruled out at 99.0% confi dence, and the best-fitting values of Omega (m) in matter are 0.10(-0.10)(0.25) and -0.25(-0.25)(+0.35) assuming zero space curvature and zero cosmol ogical constant, respectively. Note that identical results obtain when the low-redshift bin, which includes Cygnus A, is excluded; these results are i ndependent of whether the radio source Cygnus A is included. The method doe s not rely on a zero-redshift normalization. The radio properties of each s ource 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 hav e physical characteristics similar to those found for the original 14 sourc es. 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 10(45 ) ergs s(-1).