Radio-optical alignments in a low radio luminosity sample

We present an optically based study of the alignment between the radio axes and the optical major axes of eight z similar to 0.7 radio galaxies in a 7 C sample. The radio galaxies in this sample are approximate to 20 times les s radio-luminous than 3C galaxies at the same redshift, and are significant ly less radio-luminous than any other well-defined samples studied to date. Using Nordic Optical Telescope images taken in good seeing conditions at r est frame wavelengths just longward of the 4000-Angstrom break, we find a s tatistically significant alignment effect in the 7C sample. Furthermore, in two cases where the aligned components are well separated from the host we have been able to confirm spectroscopically that they are indeed at the sa me redshift as the radio galaxy. However, a quantitative analysis of the al ignment in this sample and in a corresponding 3C sample from HST archival d ata indicates that the percentage of aligned flux may be lower and of small er spatial scale in the 7C sample. Our study suggests that alignments on th e 50-kpc scale an probably closely related to the radio luminosity, whereas those on the 15-kpc scale are not. We discuss these results in the context of popular models for the alignment effect.