QUINTESSENCE, COSMOLOGY, AND FANAROFF-RILEY TYPE IIb RADIO GALAXIES

Fanaroff-Riley type IIb (FR IIb) radio galaxies provide a modified standard yardstick that allows con-straints to be placed on global cosmological parameters. This modified standard yardstick is analogous to the modified standard candle provided by Type Ia supernovae. The radio galaxy and supernovamethods provide a measure of the coordinate distance to high-redshift sources, and the coordinate distance is a function of global cosmological parameters. A sample of 20 FR IIb radio galaxies with redshifts between 0 and 2 are compared with the parent population of 70 radio galaxies to determine the coordinate distance to each source. The coordinate-distance determinations are used to constrain the current mean mass-energy density of quintessence Q, the equation of state of the quintessence w, and the current mean mass-energy density of nonrelativistic matter m; zero space curvature is assumed. Radio galaxies alone indicate that the universe is currently accelerating in its expansion (with 84 % confidence); most of the allowed parameter space falls within the accelerating universe region on the m-w plane. This provides verification of the acceleration of the universe indicated by high-redshift supernovae and suggests that neither method is plagued by systematic errors. It is found that mmust be less than about 0.5 and the equation of state w of the quintessence must lie between0.25 and2.5 at about 90 % confidence. Fits of the radio galaxy data constrain the model parame