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Visibility of scattered broad-line emission in Seyfert 2 galaxies

机译：Seyfert 2星系中散布的宽谱线发射的可见性

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摘要

Active galaxies are thought to be powered by the accretion of gas onto a central massive black hole. Seyfert galaxies—the most common examples of nearby active galaxies—are separated into two classes based on their emission line widths. Seyfert 1 galaxies exhibit broad emission lines that are attributed to ionized gas within 1 pc of the black hole, whereas the spectra of Seyfert 2 galaxies show only narrower emission lines, believed to originate from a much larger region around the core. The 'unified model' for Seyfert galaxies attributes these differences to the presence of a dusty torus of dense molecular gas surrounding the black hole: the orientation of Seyfert 2 galaxies is such that the broad-line region is obscured. The detection in the polarization spectrum of broad emission lines scattered into our line of sight by free electrons in NGC1068 (the prototypical Seyfert 2 galaxy) and other Seyfert 2 galaxies has strengthened this view, but all of these galaxies were subject to selection biases. Here we report the results of a systematic search for polarized broad emission lines in a well defined sample of Seyfert 2 galaxies. We show that the ability to detect scattered broad emission lines is related to the far-infrared colours, in the manner predicted by the unified model.
机译：活跃的星系被认为是由气体在中央大质量黑洞上的积聚提供动力的。塞弗特星系-附近活跃星系的最常见示例-根据其发射线宽度分为两类。塞弗特1星系显示出宽的发射线，这归因于黑洞1 pc内的电离气体，而塞弗特2星系的光谱仅显示了更窄的发射线，据信其起源于核周围更大的区域。塞弗特星系的“统一模型”将这些差异归因于围绕黑洞的尘埃分子气体的尘埃圆环的存在：塞弗特2星系的方向使得宽线区域被遮盖。 NGC1068（典型的赛弗2号星系）和其他赛弗2号星系中的自由电子对散射到我们视线中的宽发射线的偏振光谱的检测加强了这种观点，但是所有这些星系都受到选择偏差的影响。在这里，我们报告了在一个明确定义的赛弗2星系样本中系统搜索极化的宽发射线的结果。我们表明，以统一模型预测的方式，检测散射的宽发射线的能力与远红外颜色有关。

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