Superdisks in radio galaxies

We present evidence for a striking new feature of powerful radio galaxies: gigantic disklike structures of thermal gas and dust oriented roughly perpe ndicular to the radio jets and situated around the elliptical host galaxy. These superdisks, or fat pancakes, appear to have a typical diameter of at least 75 kpc and a width of similar to 25 kpc. Quite plausibly, they are ti dally stretched remnants of gas rich disk galaxies, or damped Lyman-alpha c louds, captured by the massive elliptical, and heated by its hot coronal ga s. Observational manifestations of the superdisks include the sharp, quasi- linear, edges of the radio lobes on the side facing the central elliptical, detected in at least a dozen well mapped radio galaxies at low to moderate redshifts. For radio galaxies with z > 1.8, evidence for superdisks is bas ed on the apparent asymmetry of diffuse Ly alpha emission associated with t he radio lobes, which is a very sensitive tracer of dust. This asymmetry ca n be understood if the brighter Ly alpha emission is associated with the ra dio lobe on the near side of the nucleus and hence not obscured by the dust in the superdisk. Superdisks can provide more consistent explanations for some of the best established correlations among the radio source properties : namely, the Laing-Garrington effect and the correlated radio-optical asym metry. They are also likely to be responsible for part of the low-frequency flux variability of compact radio sources. We argue they may provide an im proved explanation of Ly alpha absorption dips in the emission profiles of distant radio galaxies. Additional methods of searching for superdisks and testing this scenario are proposed.