Quintessence, Cosmology, and Fanaroff-Riley Type II[CLC]b[/CLC] Radio Galaxies

Fanaroff-Riley type IIb (FR IIb) radio galaxies provide a modified standardyardstick that allows constraints to be placed on global cosmologicalparameters. A sample of 20 FR IIb radio galaxies with redshifts between 0 and 2are compared with the parent population of 70 radio galaxies to determine thecoordinate distance to each source. The coordinate-distance determinations areused to constrain the current mean mass-energy density of quintessence$\Omega_q$, the equation of state of the quintessence w, and the current meanmass-energy density of nonrelativistic matter $\Omega_m$; zero space curvatureis assumed. Radio galaxies alone indicate that the universe is currentlyaccelerating in its expansion (with 84% confidence); most of the allowedparameter space falls within the accelerating universe region on the$\Omega_m$-w plane. This provides verification of the acceleration of theuniverse indicated by high-redshift supernovae and suggests that neither methodis plagued by systematic errors. It is found that $\Omega_m$ must be less thanabout 0.5 and the equation of state w of the quintessence must lie between-0.25 and -2.5 at about 90% confidence. Fits of the radio galaxy data constrainthe model parameter $\beta$, which describes a relation between the beam powerof the active galactic nucleus (AGN) and the total energy expelled throughlarge-scale jets. It is shown that the empirically determined model parameteris consistent with models in which the outflow results from the electromagneticextraction of rotational energy from the central compact object. A specificrelation between the strength of the magnetic field near the AGN and the spinangular momentum per unit mass of the central compact object is predicted