Fe ii emission spectra in AGN: observations and theoretical interpretation
Fe ii emission spectra in AGN: observations and theoretical interpretation
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AGN 中的 Fe ii 发射光谱：观测和理论解释
DOI：
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发表时间：
2009
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通讯作者：
B. Peterson
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作者：
E. Verner;F. Bruhweiler;S. Johansson;B. Peterson
相对于O和Mg等α元素，Fe的富集代表了一种测量准恒星物体（QSO）宿主星系年龄和探测早期宇宙核合成的潜在手段。qso在紫外波段表现出明显的feii特征和mgi2800 Å共振双重态发射。尽管化学进化模型预测Fe/Mg丰度比随着红移的增加而降低，但QSO Fe ii (UV)/Mg ii发射线比的测量结果显示，在1到20之间存在较大的散射，在z ~ 6.4之间没有红移依赖性。在使用feii发射作为丰度指标之前，必须确定feii发射随物理条件的变化情况。我们建立了一个830能级的feii模型原子，并将其应用于光离程序中计算了feii的发射。该模型比以前的研究更复杂，使用了最新的实验室原子数据，并包括了量子粒子群中对强辐射场敏感的许多跃迁。预测的Fe ii(UV)/Mg ii比率和通量强烈依赖于非丰度因素，如微湍流、电离通量和氢密度；在得出准确的丰度之前，必须考虑所有因素。我们的计算表明，在活动星系核（AGN）宽发射线区域（blr）的密度下，Fe ii是主要的冷却剂，并且必须包括在光电离模型中。我们与隆德大学的光谱学家的密切合作对我们的Fe ii模型的进一步发展非常有益，最重要的是通过原子数据研究将Fe ii的高能水平联系起来。对feii原子结构的进一步研究是必要的，以提高我们对AGN连续体的理解，通过考虑feii伪连续体的影响，它覆盖了从1000到10000的QSO光谱Å。预测的feii发射光谱，适用于AGN中的blr，可在http://iacs.cua.edu/people/verner/Feii上获得。
The enrichment of Fe, relative to alpha elements such as O and Mg, represents a potential means to measure the ages of quasi-stellar object (QSO) host galaxies and probe nucleosynthesis in the early universe. QSOs exhibit prominent Fe ii features and Mg ii 2800 Å resonance doublet emission in the ultraviolet. Although chemical evolutionary models predict that the Fe/Mg abundance ratio decreases with increasing redshift, measurements of QSO Fe ii (UV)/Mg ii emission line ratios show large scatter from 1 to 20, with no redshift dependency up to z∼6.4. Before using Fe ii emission as an abundance indicator, one must ascertain how Fe ii emission varies with physical conditions. We have constructed an 830-level model atom for Fe ii and used it in a photoionization code to calculate Fe ii emission. This model is more sophisticated than previous efforts, and uses the most recent laboratory atomic data and includes the numerous transitions that are sensitive to the strong radiation field in QSOs. Predicted Fe ii(UV)/Mg ii ratios and fluxes strongly depend on non-abundance factors such as microturbulence, ionizing flux, and hydrogen density; all must be taken into account before any accurate abundance can be derived. Our calculations show that Fe ii is the dominant coolant at densities found in active galactic nucleus (AGN) broad emission line regions (BLRs), and must be included in photoionization modelling. Our close collaboration with spectroscopists at Lund University has been highly beneficial for further development of our Fe ii model, most importantly through atomic data studies that link high-energy levels in Fe ii. Additional studies of the atomic structure of Fe ii are necessary to improve our understanding of the AGN continua by accounting for the effects of the Fe ii pseudo-continuum, which blanket QSO spectra from 1000 to 10 000 Å. Predicted Fe ii emission spectra, suitable for BLRs in AGN, are available at http://iacs.cua.edu/people/verner/Feii.