The estimate of kinetic power of jets in FR II radio galaxies: Existence of invisible components?

We investigate the total kinetic power (L_j) and age (t _age) of powerful jets in FR II radio galaxies by comparison of the dynamical model of expanding cocoons with observations. We select four FR II radio sources (Cygnus A, 3C 223, 3C 284, and 3C 219), for which the mass-density profiles of the intracluster medium (ICM) are known in the literature. It is found that large fractions ≳0.02-0.7 of the Eddington luminosity (L _Edd) are carried away as kinetic power of jets. The upper limit of estimated 2L_j/L_Edd is larger than unity (≲10) for some sources, suggesting the possibility of super-Eddington mass accretions. As a consequence of the large powers, we also find that the total energy stored in the cocoon (E_c) exceeds the energy derived from the minimum energy condition for the energy of radiating nonthermal electrons and magnetic fields (E_mim): 4 < E_c/E_mim < 310. This implies that most of the energy in the cocoon is carried by invisible components such as thermal leptons (electron and positron) and/or protons.