Starbursts and the origins of the activity in nearby powerful radio galaxies

We present WHT spectropolarimetry observations of a complete RA-limited sample of nine low-redshift (0.05 < z < 0.2) 3CR radio sources in order to investigate the nature of the UV excess in nearby powerful radio galaxies. Of these nine galaxies, we find that four show a measurable UV excess following nebular continuum subtraction, but none of the sources shows significant polarization in the UV. One of the radio galaxies with a UV excess-3C184.1-shows evidence for broad permitted lines and hence direct AGN light. In the remaining three galaxies we argue that the most likely contributor to the UV excess, since both direct and scattered AGN light can be eliminated, is a young stellar component. The continuum spectral energy distribution (SED) of each galaxy has been modeled, and for these three galaxies we find the best-fitting model to consist of a combination of an old stellar population plus a reddened young stellar population. The reddened young stellar component typically accounts for approximately half of the total flux at 4780 Angstrom, following nebular continuum subtraction.