GTC optical imaging of extremely red 5C radio galaxies at high redshift

TL;DR

This study uses GTC optical imaging to analyze seven extremely red high-redshift radio galaxies from the 5C catalog, revealing extended optical emission and potential radio-optical alignment, with indications of young stars or nuclear radiation influence.

Contribution

First optical imaging of these red radio galaxies with GTC, showing extended emission and possible alignment effects, providing insights into their nature and stellar populations.

Findings

All seven galaxies detected in g-band

Extended optical emission observed in all targets

Possible radio-optical alignment detected

Abstract

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.