Observational model of the ionized gas in Seyfert and radio-galaxy nuclei.
Observational model of the ionized gas in Seyfert and radio-galaxy nuclei.
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DOI：
10.1073/pnas.75.2.540
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发表时间：
1978-02
影响因子：
11.1
通讯作者：
D. Osterbrock
中科院分区：
文献类型：
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作者：
D. Osterbrock
在Seyfert 1、Seyfert 2和中型Seyfert星系中，用无特征连续体表示的总发射线Hbeta的等效宽度都具有近似相同的频率分布。这表明窄线低密度气体和宽线高密度气体的能量输入机制都是被无特征连续体光电离。在极端的塞弗特1星系中，狭窄的发射线之所以弱，是因为靠近中心源的致密气体吸收了大部分电离光子。采用典型旋转速度为5000 km/s，典型湍流速度为2000 km/s的模型可以拟合线宽的统计量。提出了致密气体形成一个旋转的湍流盘的模型，其尺寸约为0.1 pc，高/直径约为2/5。塞弗特2星系是具有少量致密气体的天体，而中等类型的塞弗特星系是这样的天体，其中的致密气体在光学上很薄，至少沿着两极的电离辐射是如此。大多数射电星系都有强而窄的发射线，这表明射电等离子体的逃逸只能发生在一些电离光子也能从致密气体中逃逸的地方。本文还讨论了该模型的其他预测、含义和检验。
Equivalent widths of the total emission-line Hbeta in Seyfert 1, Seyfert 2, and intermediate-type Seyfert galaxies, expressed in terms of the featureless continuum, all have approximately the same frequency distribution. This suggests that the energy-input mechanism to both the narrow-line, low-density gas and the broad-line, high-density gas is photoionization by the featureless continuum. The reason for the weakness of the narrow emission lines in extreme Seyfert 1 galaxies is then the absorption of most of the ionizing photons in the dense gas near the central source. The statistics of line widths can be fitted by a model in which the dense gas has typical rotational velocity 5000 km/sec and typical turbulent velocity 2000 km/sec. A model is proposed in which the dense gas forms a rotating, turbulent disk with dimension approximately 0.1 pc and height/diameter approximately 2/5. Seyfert 2 galaxies are objects with little dense gas, and intermediate-type Seyfert galaxies are objects in which the dense gas is optically thin to ionizing radiation at least along the poles. Most radio galaxies have strong narrow emission lines, suggesting that escape of radio plasma can only occur where some ionizing photons can also escape from the dense gas. Other predictions, implications, and tests of this model are discussed.