Recent improvements to atomic energy-level data allow, for the first time, accurate predictions to be made for the Fe III line emission strengths in the spectra of luminous, Lbol≃1046−1048ergs−1⁠, active galactic nuclei. The Fe III emitting gas must be primarily photoionized, consistent with observations of line reverberation. We use CLOUDY models exploring a wide range of parameter space, together with ≃26 000 rest-frame ultraviolet spectra from the Sloan Digital Sky Survey, to constrain the physical conditions of the line emitting gas. The observed Fe III emission is best accounted for by dense (nH ≃ 1014 cm−3) gas which is microturbulent, leading to smaller line optical depths and fluorescent excitation. Such high density gas appears to be present in the central regions of the majority of luminous quasars. Using our favoured model, we present theoretical predictions for the relative strengths of the Fe III UV34 λλ1895, 1914, 1926 multiplet. This multiplet is blended with the Si III] λ1892 and C III] λ1909 emission lines and an accurate subtraction of UV34 is essential when using these lines to infer information about the physics of the broad line region in quasars.

中文翻译：

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类星体中的 Fe iii 发射：密集湍流介质的证据

最近对原子能级数据的改进首次允许对发光的 Lbol≃1046−1048ergs−1⁠ 活动星系核光谱中的 Fe III 线发射强度进行准确预测。Fe III 发射气体必须主要是光电离的，与线混响的观察结果一致。我们使用探索广泛参数空间的 CLOUDY 模型，以及来自 Sloan 数字巡天的 ≃26 000 静止帧紫外光谱，来约束线发射气体的物理条件。观察到的 Fe III 发射最好由微湍流的致密 (nH ≃ 1014 cm-3) 气体来解释，导致更小的线光学深度和荧光激发。这种高密度气体似乎存在于大多数发光类星体的中心区域。使用我们喜欢的模型，我们对 Fe III UV34 λλ1895, 1914, 1926 多重峰的相对强度进行了理论预测。该多重峰与 Si III] λ1892 和 C III] λ1909 发射线混合，当使用这些线来推断类星体中宽线区域的物理信息时，准确减去 UV34 是必不可少的。