GTC optical imaging of extremely red 5C radio galaxies at high redshift
  We investigate the nature of seven unusual radio galaxies from the 5C
catalogue that were previously known to have extremely red R-K colours, and for
which emission lines were previously found to be weak or absent in their
optical spectra. We present and discuss u, g, or r images of these radio
galaxies, obtained using the Optical System for Imaging and
low-Intermediate-Resolution Integrated Spectroscopy (OSIRIS) at the Gran
Telescopio Canarias (GTC). We have detected all seven targets in our g-band
imaging. Their optical emission is extended, and we tentatively detect a
radio-optical alignment effect in this sample. A subset of our sample (three
sources) shows broad-band spectral energy distributions that flatten out near
the wavelength range of the g-band, implying a dominant contribution there due
to young stars and/or scattered or reprocessed radiation from the active
nucleus.
