Current status of the Big Trio search program for distant radio galaxies. New radio data

The Big Trio programme was aimed to search for distant radio galaxies for the purpose of cosmological research. A selection of sources with steep and ultra-steep spectra was made from the radio sources discovered in a series of surveys by the Cold Experiment, which was carried out on the RATAN-600 radio telescope. The results of the studies of 113 sources in this sample were the optical identification of almost the entire sample, spectral studies of the majority of the objects (70%), spectral redshift determinations for half of them, and the discovery of three unique radio galaxies with redshifts $z>3$ and extremely high radio luminosities. New radio sky surveys with high sensitivity and angular resolution have now become available, allowing additional studies of the radio sources in the sample. These have helped to refine the continuous spectra of the sources and their radiomorphology, as well as the evolutionary state and environment of the radio galaxies. The spectral indices determined from the new radio survey data turned out to be flatter than those from the old data. Based on the spectral curvature parameter and the morphological structure of the sources in the steep spectrum (SS) sample, 10–15% are likely to be young, 40–50% are in an active state, 10% are in the fading phase, and most likely 20–25% are in the restart phase.