The N?V emission line of active galactic nuclei shows peculiar behavior in the line-continuum correlation, which may be indicative of an extra line component in addition to that from the normal broad emission line region. In this paper, we investigate possible contribution to the N?V emission via resonant scattering of both continuum and Lyα in a broad absorption line (BAL) outflow by performing the Sobolev Monte Carlo simulations. The contribution is dependent on the covering factor, optical depth, and velocity profile of the outflow, as well as the equivalent width (EW) of Lyα. Adopting model parameters constrained by observations, we find that the measured N?V EW in the spectra of non-BAL quasi-stellar objects (QSOs) could have been enhanced by a factor of 1.82-2.73 on average, while there is only moderate absorption of Lyα along the BAL outflow direction. Our model can produce a relatively narrow scattering line profile. About 80% of the total scattered flux falls within the central ±4500 km s-1. We find that the resonant scattering can produce a prominent polarized emission line around N?V. Both the broad excess emission and the unusually large polarized flux observed around N?V in BAL QSOs are considered as strong evidence for the scattering enhancement. Future spectropolarimetric observations and spectroscopic monitoring of luminous QSOs may offer crucial tests for this interpretation, and provide useful information on the physical and geometrical properties of QSO outflows. We argue that the scattering offers a promising and robust process for producing the peculiar behavior of N?V emission compared to the other processes proposed previously.
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机译：活跃银河核的N？V发射谱线与谱线连续相关，表现出特殊的行为，这可能表明除了正常的宽发射谱线区域之外，还有额外的谱线成分。在本文中，我们通过进行Sobolev蒙特卡洛模拟研究了连续吸收体和Lyα在宽吸收线（BAL）流出中通过共振散射对NV发射的可能贡献。贡献取决于覆盖因子，光学深度和流出速度分布以及Lyα的等效宽度（EW）。采用受观测约束的模型参数，我们发现在非BAL准星体（QSOs）光谱中测得的N？V EW平均可以提高1.82-2.73倍，而只有中等吸收Ly沿BAL流出方向的变化。我们的模型可以产生相对较窄的散射线轮廓。总散射通量的大约80％落在中心±4500 km s-1之内。我们发现共振散射可以在N？V附近产生一条明显的极化发射线。在BAL QSO中，在N？V附近观察到宽泛的过量发射和异常大的极化通量，都被认为是散射增强的有力证据。发光QSO的未来光谱极化观测和光谱监视可能会为这种解释提供关键测试，并提供有关QSO流出物的物理和几何特性的有用信息。我们认为，与先前提出的其他过程相比，散射为产生NV发射的特殊行为提供了一种有前途且强大的过程。
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