Radio properties of high-redshift galaxies at $z\ge 1$

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 $z⩾1$ with flux densities $S_{1.4}⩾20$ 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 sources 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 for our sample compared to high-redshift quasars at $z\ge 3$. The variety of the obtained radio properties shows the different conditions for the formation of radio emission sources in galaxies.

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