Radio Properties of High-Redshift Galaxies at \(\boldsymbol{z\geq 1}\)

Abstract

Study of high-redshift radio galaxies (HzRGs) can shed light on the active galactic nuclei (AGNs) evolution in massive elliptical galaxies. The vast majority of observed high-redshift AGNs are quasars, and there are very few radio galaxies at redshifts \(z>3\). We present the radio properties of 173 sources optically identified with radio galaxies at \(z\geq 1\) with flux densities \(S_{1.4}\geq 20\) mJy. Literature data were collected for compilation of broadband radio spectra, estimation of radio variability, radio luminosity, and radio loudness. Almost 60\(\%\) of the galaxies have steep or ultra-steep radio spectra; 22\(\%\) have flat, inverted, upturn, and complex spectral shapes, and 18\(\%\) have peaked spectra (PS). The majority of the PS sources in the sample (20/31) are megahertz-peaked spectrum source candidates, i.e. possibly very young and compact radio galaxies. The median values of the variability indices at 11 and 5 GHz are \(V_{S_{11}}=0.14\) and \(V_{S_{5}}=0.13\), which generally indicates a weak or moderate character of the long-term variability of the studied galaxies. The typical radio luminosity and radio loudness are \(L_{5}=10^{43}{-}10^{44}\) erg s\({}^{-1}\) and \(\log R=3{-}4\) respectively. We have found less prominent features of the bright compact radio cores in our sample compared to high-redshift quasars at \(z\geq 3\). The variety of the obtained radio properties shows the different conditions for the formation of radio emission sources in galaxies.