Radio properties of high-redshift galaxies at z≥1

Khabibullina M.; Mikhailov A.; Sotnikova Yu.; Mufakharov T.; Mingaliev M.; Kudryashova A.; Bursov N.; Stolyarov V.; Udovitskij R.

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 logR=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≥3. The variety of the obtained radio properties shows the different conditions for the formation of radio emission sources in galaxies.