AGN-environment interplay observed at ultra-low radio frequencies

众所周知，活动星系核（AGN）可以通过释放大量能量来影响周围环境。它们的作用影响范围很广，甚至星系团的宇宙学演化也受到AGN反馈的影响。虽然科学界很久以前就认识到AGN效应是星系和星系团演化的一个关键因素，但AGN活动与周围环境之间的相互作用是复杂的，这种相互作用的长期影响很难在观测上加以限制。AGN的反馈是由从中央发动机传输能量的磁化等离子体射流介导的。观测追踪喷出的等离子体对于测量(i) AGN对环境的影响以及（ii）环境如何塑造来自AGN的等离子体的特性至关重要。幸运的是，存在于这些等离子体中的相对论性宇宙射线（CR）电子在无线电波段辐射。电子的能量越低，这种无线电同步加速器发射的频率就越低。本文旨在通过超低频射电观测，绘制AGN起源CR的空间和能量分布图。因此，我们将能够看到AGN与周围介质之间的长期（数百迈尔）相互作用。从历史上看，无线电频率的深度和高分辨率观测只能在千兆赫频率上进行。随着新型设备的出现，如低频阵列（LOFAR），低（<1 GHz）甚至超低（<100 MHz）无线电频率的窗口现在已经准备好探索。

It is well known that active galactic nuclei (AGN) can influence the surrounding environment by releasing a large quantity of energy. Their action affects a wide range of scales, so that even the cosmological evolution of galaxy clusters is influenced by AGN feedback. While the scientific community has recognised long time ago that AGN effect is a crucial piece of the puzzle for galaxy and galaxy cluster evolution, the interplay between AGN activity and the surrounding environment is complex and the long-term effect of this interaction is difficult to constrain observationally. AGN feedback is mediated by jets of magnetised plasma that transport energy away from the central engine. Tracing observationally the ejected plasma is crucial to measure (i) the effect of the AGN on the environment and (ii) how the environment shapes the properties of the plasma from AGN. Fortunately, relativistic cosmic ray (CR) electrons present in these plasmas radiate in the radio band. The lower the energy of the electrons, the lower the frequency of this radio synchrotron emission. Here we aim to chart the spatial and energetic distribution of CR of AGN origin through ultra-low frequency radio observations. Thus, we will be able to look at the long-term (hundreds of Myr) interplay between AGN and the surrounding medium. Historically, deep and high-resolution observations at radio frequencies were only possible at GHz frequencies. With the advent of novel facilities, such as the Low Frequency Array (LOFAR),the window of low- (<1 GHz) and even ultra-low- (<100 MHz) radio frequencies is now ready to be explored.