THE MAGNETIZATION OF THE INTERGALACTIC MEDIUM BY EXTRAGALACTIC JETS

Observational studies indicate evidence for the magnetization of the intracluster medium for some clusters of galaxies, whereas it is still an open question if the intercluster medium is permeated by magnetic fields. The origin at the intracluster media magnetization is not solved yet. Existing theories proposed up to now, and their limitations, are briefly discussed. We propose an alternative theory based on the observed common phenomenon of extragalactic jets (EJ). We consider the time evolution of a current carrying EJ, and the associated return current closing the circuit. For the return path, the Lorentz force is expansive. We assume that such an expansion occurs at the local Alfven velocity and calculated numerically the radial distance from the jet axis which the return circuit reaches. Calculations are made for parameter values observed for the extragalactic sources Cygnus A, NGC 6251, 3C465 and M84. The results obtained can explain several magnetic features observed in these sources. The possible importance of previous generations of EJ in the large scale magnetization of the intergalactic medium is also discussed.