Associated with one of the most important forms of active galactic nucleus (AGN) feedback, and showing a strong preference for giant elliptical host galaxies, radio AGN ($$L_{1.4\,\mathrm{GHz}} > 10^{24}$$L1.4GHz>1024 W $$\hbox {Hz}^{-1}$$Hz-1) are a key sub-class of the overall AGN population. Recently their study has benefitted dramatically from the availability of high-quality data covering the X-ray to far-IR wavelength range obtained with the current generation of ground- and space-based telescope facilities. Reflecting this progress, here I review our current state of understanding of the population of radio AGN at low and intermediate redshifts ($$z < 0.7$$z<0.7), concentrating on their nuclear AGN and host galaxy properties, and covering three interlocking themes: the classification of radio AGN and its interpretation; the triggering and fuelling of the jet and AGN activity; and the evolution of the host galaxies. I show that much of the observed diversity in the AGN properties of radio AGN can be explained in terms of a combination of orientation/anisotropy, mass accretion rate, and variability effects. The detailed morphologies of the host galaxies are consistent with the triggering of strong-line radio galaxies (SLRG) in galaxy mergers. However, the star formation properties and cool ISM contents suggest that the triggering mergers are relatively minor in terms of their gas masses in most cases, and would not lead to major growth of the supermassive black holes and stellar bulges; therefore, apart from a minority (<20 %) that show evidence for higher star formation rates and more massive cool ISM reservoirs, the SLRG represent late-time re-triggering of activity in mature giant elliptical galaxies. In contrast, the host and environmental properties of weak-line radio galaxies (WLRG) with Fanaroff–Riley class I radio morphologies are consistent with more gradual fuelling of the activity via gas accretion at low rates onto the supermassive black holes.

中文翻译：

---

本地宇宙中的无线电 AGN：统一、触发和演化

与活动星系核 (AGN) 反馈的最重要形式之一相关，并表现出对巨型椭圆宿主星系的强烈偏好，无线电 AGN ($$L_{1.4\,\mathrm{GHz}} > 10^{24} $$L1.4GHz>1024 W $$\hbox {Hz}^{-1}$$Hz-1) 是整个 AGN 人口的一个关键子类。最近，他们的研究极大地受益于覆盖 X 射线到远红外波长范围的高质量数据的可用性，这些数据是通过当代地面和空间望远镜设施获得的。反映这一进展，我在这里回顾了我们目前对低红移和中红移（$$z < 0.7$$z<0.7）射电 AGN 种群的理解状态，重点关注它们的核 AGN 和宿主星系特性，并涵盖三个互锁主题：无线电AGN的分类及其解释；喷射和 AGN 活动的触发和燃料；以及宿主星系的演化。我表明，在无线电 AGN 的 AGN 属性中观察到的大部分多样性可以用方向/各向异性、质量吸积率和可变性效应的组合来解释。宿主星系的详细形态与星系合并中强线射电星系（SLRG）的触发一致。然而，恒星形成特性和冷 ISM 含量表明，在大多数情况下，触发合并的气体质量相对较小，不会导致超大质量黑洞和恒星凸起的大量增长；因此，除了少数 (<20%) 显示出更高的恒星形成率和更大质量的冷 ISM 储层的证据，SLRG 代表了成熟巨椭圆星系中活动的后期重新触发。相比之下，具有 Fanaroff-Riley I 类射电形态的弱线射电星系 (WLRG) 的宿主和环境特性与通过气体以低速率吸积到超大质量黑洞上的活动更加渐进相一致。