UNIFIED SCHEMES FOR RADIO-LOUD ACTIVE GALACTIC NUCLEI
UNIFIED SCHEMES FOR RADIO-LOUD ACTIVE GALACTIC NUCLEI
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DOI：
10.1086/133630
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发表时间：
1995-06
影响因子：
3.5
通讯作者：
C. Urry;P. Padovani
中科院分区：
文献类型：
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作者：
C. Urry;P. Padovani
活动星系核（AGN）的出现强烈依赖于方向，我们目前的分类方案是由随机指向的方向，而不是更有趣的物理性质占主导地位。来自许多活动星系核中心的光被光学厚的星周物质遮蔽，特别是在光学和紫外波长。在射电强活动星系核中，从原子核发出的双极喷流通过相对论性地沿喷流轴沿着传播的伽马射线发出射电。了解活动星系核辐射各向异性的起源和大小，使我们能够统一不同类别的活动星系核;也就是说，识别每一个单一的，潜在的活动星系核类型，通过不同的方向产生不同的类别。本文综述了射电星系、类星体和耀变体的射电活动星系核的统一。我们描述了活动星系核的分类和一般性质。我们总结的证据，各向异性发射所造成的拱星遮蔽和相对论性光束。我们概述了两个最合理的无线电响亮AGN的统一计划，一个连接高光度源（BL Lac对象和不太明亮的射电星系）。使用适当的形式主义的样本偏置相对论性光束，我们表明，人口统计两个计划是根据现有的数据。我们分析了低光度和高光度射电活动星系核之间可能存在的联系，并得出结论，它们可能是由类似的物理过程提供动力的，至少在相对论喷流中是这样。我们审查了统一的潜在困难，并得出结论，目前没有一个构成严重问题。我们讨论了可能的并发症，以统一的计划，建议现实的物理考虑，这些将是重要的考虑时，更全面的数据，更大的完整的样本变得可用。最后，我们列出了我们认为在这一领域最紧迫的十个问题。
The appearance of active galactic nuclei (AGN) depends so strongly on orientation that our current classification schemes are dominated by random pointing directions instead of more interesting physical properties. Light from the centers of many AGN is obscrued by optically thick circumstellar matter, particularly at optical and ultraviolet wavelengths. In radio-loud AGN, bipolar jets emanating from the nucleus emit radio through gamma-ray light that is relativistically beamed along the jet axes. Understanding the origin and magnitude of radiation anistropies in AGN allows us to unify different classes of AGN; that is, to identify each single, underlying AGN type that gives rise to different classes through different orientations. This review describes the unification of radio-loud AGN, which includes radio galaxies, quasars, and blazars. We describe the classification and general properties of AGN. We summarize the evidence for anisotropic emission caused by circumstellar obscuration and relativistic beaming. We outline the two most plausible unified schemes for radio-loud AGN, one linking the high-luminosity sources (BL Lac objects and less luminous radio galaxies). Using the formalism appropriate to samples biased by relativistic beaming, we show the population statistics for two schemes are in accordance with available data. We analyze the possible connections between low- and high-luminosity radio-loud AGN and conclude they probably are powered by similar physical processes, at least within the relativistic jet. We review potential difficulties with unification and conclude that none currently constitutes a serious problem. We discuss likely complications to unified schemes that are suggested by realistic physical considerations; these will be important to consider when more comprehensive data for larger complete samples become available. We conclude with a list of the ten questions we believe are the most pressing in this field.