Radio and X-Ray Observations of Large Scale Jets in Quasars

Extract

The first big radio jet to be found in a quasar was in 4C32.69 (z=.659) (Potash and Wardle, 1980). A new higher resolution map of this jet, made with the VLA at 5 GHz, is shown in Fig. 1. Observationally the important points are 1) it is very luminous, 2) it is very well collimated, 3) the magnetic field is parallel to the jet over its entire length, 4) it bends at least three times along its path to the outer radio lobe. Physically this is interesting because 1) it is a very lossy pipeline to the outer lobe, 2) the high degree of collimation suggests either the jet is confined by external pressure or it is highly supersonic. But the minimum internal energy density is very high (>3×10^–10 erg cm^–3), so if it is confined the external pressure must also be very high. On the other hand, if the jet is expanding freely, it is easy to show that the momentum flux is enormous (>4×10³⁸ dynes). Such a jet is very rigid. It is difficult to stop and difficult to bend, but evidently both of these things happen. A detailed discussion of these problems is given in Potash & Wardle (1980), who concluded that the jet cannot be expanding freely. They suggested that the jet might be confined either by the thermal pressure of external hot gas, or by a helical component of magnetic field due to currents in the jet.