Depolarization silhouettes and the filamentary structure in the radio source Fornax A

The giant radio source Fornax A was imaged with the VLA at 1.5 GHz with a resolution of 14 arcsec, corresponding to 2.2 kpc. It is identified with the 9th mag cD galaxy, NGC 1316, in a poor cluster. Within the radio lobes are several depolarized regions, one of which is the silhouette of the foreground spiral galaxy, NGC 1310, in the same group. The other depolarization regions are not associated with visible objects. If they are also produced by intervening material in the cluster, they would contain the mass of a typical galaxy. The lobes have unprecedented filamentary structure which is polarized and well organized; the origin of the filaments is unknown. The galaxy has an extended envelope whose edge corresponds with the inner boundary of the radio lobes. 30 refs