New Radio Data on Sources of the Big Trio Program for Searching for Distant Radio Galaxies

Abstract

Radio sources with steep and ultra-steep spectra, identified through a series of surveys of the Cold experiment using the RATAN-600 radio telescope, formed the basis of the Big Trio program aimed at discovering distant radio galaxies. With the advent of new radio, optical, and infrared sky surveys, it became possible to carry out additional studies of the 113 radio sources observed within this program using the 6-meter BTA telescope. Morphological features indicative of the evolutionary state of radio sources revealed that 9 objects exhibit signs of restarted activity, 12 can be classified as young, and 2 as dying. Based on their WAT/NAT and WRS morphologies, 24 sources are likely located within galaxy groups or clusters, or show evidence of jet reorientation. Additionally, four objects in the sample represent pairs of radio sources whose host galaxies are separated by only a few tens of kiloparsecs. Continuum spectra were constructed, and variability indices were calculated. A high proportion of sources with a variability index ($V>3$) is attributed to significant differences in angular resolution between the TXS and VCSS surveys, as well as to underestimated flux densities for certain double-lobed sources. A comparison of spectral indices derived from older and newer data indicates a decrease in the number of steep-spectrum sources in the sample. This reduction is most likely due to improved characterization of the low-frequency portion of the continuum spectra following the incorporation of GLEAM data. However, for some radio sources, the observed spectral changes may reflect internal evolution, that observed in a shift of the spectral peak or a roll-off in the radio spectrum towards lower frequencies, as evidenced by flux density measurements from various catalogues covering a period of up to forty years.