The nebular contribution to the extended UV continua of powerful radio galaxies

Abstract

We investigate the nebular contribution to the extended UV continua of three high/intermediate-redshift radio galaxies: PKS 2250-41 (z=0.310), 3C 368 (z=1.132) and 4C 41.17 (z=3.8). Using the measured emission-line fluxes, we show that the nebular continuum emitted by the warm gas contributes as much as 60 per cent of the observed UV continua. The nebular component is likely to be important wherever emission lines of large equivalent width are observed; its presence helps to explain the lower-than-expected UV polarizations measured in many radio galaxies.