活动星系的电磁波谱考古学
Archaeology of active galaxies across the electromagnetic spectrum
摘要：
分析和数值的星系形成模型表明，活动星系核（AGN）可能在星系的形成和演化中起着重要的作用。然而，量化这种影响需要了解星系在整个生命周期中核活动如何进行，是否与静止期交替，如果是这样，这些周期发生的时间尺度。这一主题引起了越来越多的兴趣，但取得进展仍然是一项具有挑战性的任务。对于光学和射电活动星系核，各种各样的技术被用来进行一种“考古学”，追踪过去核活动的特征。在这里，我们总结了最近的发现，关于生命周期的活动星系核的光学和无线电观测。到目前为止，我们所掌握的有限的情况表明，这些周期可以从10^7-10^8年的长周期到10^4-10^5年的短周期，甚至在短短几年的时间尺度上达到极端事件。与模拟一起，关于活动星系核活动的多个周期的观测结果有助于创建活动星系核生命周期的完整图片。
英文摘要：
Analytical and numerical galaxy-formation models indicate that active galactic nuclei (AGNs) likely play a prominent role in the formation and evolution of galaxies. However, quantifying this effect requires knowledge of how the nuclear activity proceeds throughout the life of a galaxy, whether it alternates with periods of quiescence and, if so, on what timescales these cycles occur. This topic has attracted growing interest, but making progress remains a challenging task. For optical and radio AGNs, a variety of techniques are used to perform a kind of "archaeology" that traces the signatures of past nuclear activity. Here we summarize recent findings regarding the lifecycle of an AGN from optical and radio observations. The limited picture we have so far suggests that these cycles can range from long periods of 10^7-10^8 yr to shorter periods of 10^4-10^5 yr, even reaching extreme events on timescales of just a few years. Together with simulations, observational results regarding the multiple cycles of AGN activity help to create a complete picture of the AGN lifecycle.
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