Abstract

We fail to detect a polarized broad line in the 2% polarized narrow line radio galaxy Cygnus A. The possible explanations are that a diluting dichroic component is present (in which case more sensitive observations should show the polarized broad line), that a hidden broad line nucleus is being scattered by electrons which smear out the broad line, or that Cygnus A really is a narrow line radio galaxy and contains no “hidden quasar”.

Introduction

There is now considerable evidence that some apparently narrow emission line objects contain hidden broad line regions. The first discovery in this field was the observation (Antonucci and Miller 1985) that the Seyfert 2 (narrow line) galaxy NGC 1068 had a broad line region in polarized light, which they interpreted as a scattered image of a broad line nucleus whose direct line of sight was blocked by an obscuring torus. Further such discoveries in Seyfert galaxies (Miller and Goodrich 1990), in one broad line radio galaxy (3C234, Antonucci 1984) and in one low–power narrow line radio galaxy (Inglis et al 1992) lend support to the idea that at least some narrow line objects would appear as broad line objects if seen from a suitable angle.

Most of the objects so far shown to contain polarized broad lines have been low–luminosity objects. Proposals that narrow–line and broad line high–luminosity, radio loud objects can be unified by a scenario such as that of Antonucci and Miller have been made over the last few years (Scheuer 1987, Peacock 1987, Barthel 1989).