Estimate of the total kinetic power and age of an extragalactic jet by its cocoon dynamics: The case of Cygnus A

Abstract

We examine the constraints imposed on the total kinetic power (L j) and the age (tage) of relativistic jets in Fanaroff-Riley type II radio sources in a new way. We solve the dynamical expansion of its cocoon embedded in the intracluster medium and obtain the analytical solution of its physical quantities in terms of Lj and tage. We estimate Lj and tage using a comparison of the model and the observed shape of the cocoon. The analysis focuses on Cygnus A and we find that (i) the source age is 3 < t age < 30 Myr and (ii) the total kinetic power of the jet is estimated as 0.2 × 1046 < Lj < 1 × 1048 erg s-1, which is larger than 1 per cent of the Eddington luminosity of Cygnus A. © 2005 RAS.