A Hidden Nucleus in Cygnus A, but Not in M87

Abstract

Historically the narrow line radio galaxies were thought to be intrinsically nonthermal, and without significant accretion. When the Unified Model came along the compelling observational motivation for this lost some force: some are found to be hidden broad line objects, and in principle that could be the case with all of them. The clear sign of a hidden quasar is a normal quasar spectrum in polarized (scattered) light. However that test requires a suitably placed "mirror." A more robust test is the high predicted mid-IR core luminosity reradiating from the obscuring matter. Cygnus A has this component, but M87 does not.