OBSERVATIONS OF INTERACTION BETWEEN CLUSTER GAS AND THE RADIO LOBES OF CYGNUS-A

We present an X-ray observation of the powerful radio galaxy Cygnus A using the ROSAT High Resolution Imager. This observation reveals clear signatures of hydrodynamic modification of the cluster gas by the jets and lobes of the radio source. There are clear deficits of X-ray surface brightness coincident with the inner radio lobes. Such deficits suggest that the thermal cluster gas is effectively excluded from the radio lobes. Likewise, there are knots of excess X-ray emission along the edges of the radio lobes, corresponding to emission by the displaced intracluster medium (ICM). These features can be explained in the context of the jet model for the hydrodynamic evolution of the radio-emitting lobes of a powerful radio source in the centre of a dense X-ray cluster. These observations provide strong support for the basic jet model for powerful radio galaxies.