Unified models for active galactic nuclei and quasars
Unified models for active galactic nuclei and quasars
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DOI：
10.1146/annurev.aa.31.090193.002353
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发表时间：
1993
影响因子：
33.3
通讯作者：
R. Antonucci
中科院分区：
文献类型：
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作者：
R. Antonucci
由于活动星系核（AGN）和类星体的临界中心区域是强烈非球形的，但空间上无法分辨，方位效应一直是许多混乱的来源。事实上，现在看来，活动星系核类型的多样性只是相对于视线方向变化的结果。我们可以定义一个极端的假设，即稻草人模型（SPM），其中活动星系核有两种基本类型：射电静噪和射电强噪。对于每种类型，都有一个内在光度范围，光度控制着一些属性，如Fanaroff和Riley类。然而，在一个给定的固有光度，所有其他属性，如光谱分类和VLBI组件的速度归因于取向。这种模式只是对统一思想的一种讽刺，而且已经被许多理由排除在外，但它将有助于组织讨论。我将描述我认为是令人信服的证据，证明方向效应是重要和普遍的。从某种意义上说，真实的情况可能介于SPM和取向根本不影响分类的假设之间。对我们这些乐观主义者来说，定向杯是半满的，而不是半空的。虽然现在下定论还为时过早，但如果从其他方向看，大多数物体的分类会有所不同的假设在今天是站得住脚的。
Because the critical central regions of Active Galactic Nuclei (AGN) and quasars are strongly nonspherical but spatially unresolved, orientation effects have been the source of much confusion. In fact, it now appears that much of the variety in AGN types is just the result of varying orientation relative to the line of sight. We can define an extreme hypothesis,, the straw person model (SPM), in which there are two basic types of AGN: the radio quiets and the radio louds. For each type there is a range in intrinsic luminosity, and the luminosity controls some properties such as the Fanaroff and Riley classes. However, at a given intrinsic luminosity, all other properties such as spectroscopic classification and VLBI component speeds are ascribed to orientation. This model is only a caricature of the unification idea, and is already ruled out on many grounds, but it will be useful for organizing the discussion. I’ll describe what I consider to be convincing evidence that orientation effects are important and widespread. The true situation may be in some sense half way between the SPM and the hypothesis that orientation doesn’t affect classification at aIl. To us optimists, the orienration cup is half full rather than half empty. Although it is too soon to say for sure, the hypothesis that most objects’ classifications would be different if seen from other directions is a tenable one today.