AGN-environment interplay observed at ultra-low radio frequencies

点击翻译按钮获取中文摘要

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.