Is the UV Alignment Effect Present in Low Redshift Radio Galaxies?

Abstract

When a FRII radio galaxy at z > 0.7 is observed in the optical, its continuum appears extended and aligned with the radio axis. This phenomenon occurs actually when the optical bands start to sample the rest-frame UV, and it was called alignment effect (McCarthy et al. 1987). The UV continuum of high z radio galaxies shows also strong linear polarization due to scattering of anisotropic radiation escaping from the obscured quasar nucleus (di Serego Alighieri, Cimatti & Fosbury 1994). However, the observations of the UV continuum have been concentrated mostly on high z radio galaxies, leaving open a main question : is the alignment effect an evolutionary phenomenon present only at high z, or is it simply a selection effect due to the K-correction ? In order to investigate the origin and evolution of the UV alignment effect, we have started a ground-based imaging and polarimetric survey for studying the UV continuum in FR II radio galaxies with 0.1 < z < 0.5. Depending on the redshift, the filters U and B can be used to sample the UV continuum free from strong emission lines, and in the same rest-frame spectral region observed in radio galaxies at higher redshift. The survey is in progress and here we present only our first results.