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.

中文翻译：

---

$$\boldsymbol{z\geq 1}$$ 处高红移星系的射电特性

摘要

高红移射电星系（HzRG）的研究可以揭示大质量椭圆星系中活动星系核（AGN）的演化。观测到的高红移活动星系核绝大多数是类星体，红移\(z>3\)的射电星系很少。我们展示了在\(z\geq 1\)处用射电星系光学识别的 173 个源的射电特性，通量密度为\(S_{1.4}\geq 20\) mJy。收集文献数据用于编制宽带无线电频谱、估计无线电变异性、无线电光度和无线电响度。几乎 60 \(\%\)的星系具有陡峭或超陡峭的射电频谱；22 个\(\%\)具有平坦、倒置、上弯和复杂的光谱形状，18 个\(\%\)具有峰值光谱(PS)。样本中的大多数 PS 源 (20/31) 是兆赫峰值频谱源候选，即可能非常年轻且紧凑的射电星系。11 和 5 GHz 的变异性指数的中值为\(V_{S_{11}}=0.14\)和\(V_{S_{5}}=0.13\)，通常表明研究星系的长期变化。典型的无线电光度和无线电响度为\(L_{5}=10^{43}{-}10^{44}\) erg s \({}^{-1}\)和\(\log R=分别为3{-}4\)。与\(z\geq 3\)处的高红移类星体相比，我们发现样本中明亮紧凑射电核心的特征不太突出。所获得的射电特性的多样性表明了星系中射电发射源形成的不同条件。