THE POLARIZED SPECTRUM OF CYGNUS-A

We report the results of a sensitive optical polarization study of the narrow line radio galaxy Cygnus A. The polarization is 2% in the blue , decreasing to 1% in the red, and most of this polarization is likely to be intrinsic to the host galaxy. No polarized broad Halpha line is found to a level of approximately 200 angstrom, and we find that the polarized intensity spectrum rises to the blue as lambda-2.8+/-0.8, Wh ich is bluer than a typical quasar spectrum. Neither electron or dust scattering alone nor foreground absorption alone is capable of reprodu cing the observations. We suggest that approximately half the polarize d spectrum is due to dust scattering and the other half to foreground extinction in the host galaxy, although we cannot entirely discount th e possibility of electron scattering.