Bloated stars as AGN broad-line clouds: the emission-line profiles
Bloated stars as AGN broad-line clouds: the emission-line profiles
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DOI：
10.1093/mnras/284.4.967
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发表时间：
1996-08
影响因子：
4.8
通讯作者：
T. Alexander;H. Netzer
中科院分区：
文献类型：
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作者：
T. Alexander;H. Netzer
“膨胀星方案”提出活动星系核宽线辐射起源于膨胀星（BS）的风或包络。亚历山大和内策尔确定，约5 × 104个具有密集、大包络的BS可以重现观测到的发射线光谱，并避免快速碰撞破坏。在这里，我们使用观测到的AGN线轮廓的属性，以进一步约束模型参数。在BS模型中，宽剖面的起源是中心黑洞附近的恒星速度场。我们使用详细的光电离程序和恒星分布函数模型计算了BS的发射线轮廓，并将它们与大样本的AGN C IV 21549，C III] 21909和Mg II 22798轮廓进行了比较。我们发现，如果（i）电离光度与黑洞质量之比足够低，（ii）宽线区的大小受到某些截断机制的限制，（iii）BS在恒星布居中的比例福尔斯近似为r- 2，（iv）风的密度和/或速度与黑洞质量和电离光度相关。在这些条件下，黑洞附近的强潮汐力在决定BS的线发射性质方面起着重要作用。仍然存在一些差异：计算的BS剖面比观测的BS剖面具有更弱的翼，并且不同谱线的剖面之间的差异比观测的稍小。
The 'bloated stars scenario' proposes that AGN broad-line emission originates in the winds or envelopes of bloated stars (BSs). Alexander & Netzer established that ~ 5 x 104 BSs with dense, large envelopes can reproduce the observed emission-line spectrum and avoid rapid collisional destruction. Here we use the observed properties of AGN line profiles to constrain the model parameters further. In the BS model, the origin of the broad profiles is the stellar velocity field in the vicinity of the central black hole. We use a detailed photo ionization code and a model of the stellar distribution function to calculate the BS emission-line profiles and compare them with a large sample of AGN C IV 21549, C III] 21909 and Mg II 22798 profiles. We find that the BSs can reproduce the general shape and width of typical AGN profiles as well as the line ratios if (i) the ionizing luminosity to black hole mass ratio is low enough, (ii) the broad-line region size is limited by some cut-off mechanism, (iii) the fraction of the BSs in the stellar population falls off roughly as r- 2, and (iv) the wind density and/or velocity are correlated with the black hole mass and ionizing luminosity. Under these conditions the strong tidal forces near the black hole play an important role in determining the line-emission properties of the BSs. Some discrepancies remain: the calculated BS profiles tend to have weaker wings than the observed ones, and the differences between the profiles of different lines are somewhat smaller than those observed.