POLARIMETRY OF THE ULTRAVIOLET CONTINUA OF SOUTHERN RADIO GALAXIES

This paper reports new B-band polarimetry measurements for four interm ediate-redshift (0.3 < z < 0.7) southern radio galaxies. Deep optical spectra show that three of these objects are broad-line radio galaxies , while the fourth is a narrow-line radio galaxy. Despite the fact tha t the measurements were made in the rest-frame ultraviolet (UV) in eac h object, and that emission-line contamination is small, we find that the majority of objects display low intrinsic continuum polarization. In two of the broad-line objects (PKS 1602 + 01 and PKS 2135 - 20), th is may result from our viewing the broad-line region directly. The sig nificant polarization measure, and corresponding polarization orientat ion, in the narrow-line object PKS 2250 - 41 is most consistent with s cattering of light from the active nucleus. We therefore identify a di versity of UV polarization properties in powerful radio galaxies at in termediate redshifts. Not all radio galaxies possess large intrinsic p olarizations. Therefore the UV excesses observed in these objects are unlikely to result solely from scattered light.