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arXiv 1106.5899astro-ph.GA
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中红外PAH特征的耦合盲信号分离与光谱数据库拟合

Coupled Blind Signal Separation and Spectroscopic Database Fitting of the Mid Infrared PAH Features

M. J. F. Rosenberg, O. Berné, C. Boersma, L. J. Allamandola, A. G. G. M Tielens

摘要:

在中红外光谱中观察到的芳香族红外带(AIB)归因于多环芳烃(PAH)。我们使用Spitzer上的红外光谱仪(IRS)在中红外(10 - 19.5微米)观察NGC 7023-西北(NW)PDR。在光谱中观察到明显的变化,最显著的是11.0至11.2微米带的比率、11.2和12.0微米带的峰位置以及11.2微米带的不对称程度。观察到的变化似乎改变作为PDR内的位置的函数。我们的目标是解释这些变化的PDR的发射组件的丰度的变化。一个盲信号分离(BSS)方法,即一个非负矩阵分解算法被应用到分离的观察到的频谱成分。利用NASA艾姆斯多环芳烃红外光谱数据库,这些提取的信号进行了拟合。单独观察到的信号也使用数据库进行拟合,并将这些分量与BSS分量进行比较。三个分量信号提取使用BSS的观察。我们将这三个信号归因于电离的多环芳烃,中性多环芳烃和非常小的颗粒(VSGs)。BSS提取的光谱与多环芳烃数据库的拟合进一步证实了电离和中性多环芳烃的归属,并提供了两种方法产生可靠结果的信心。11.0微米的特征归因于PAH阳离子,而11.2微米的带归因于中性PAH。VSG信号在11.3微米处显示出具有延伸的红色翼的特征性非对称宽特征。将NASA Ames多环芳烃红外光谱数据库与BSS方法相结合,可以确认各方法的独立结果,克服各方法的局限性。

英文摘要:

The aromatic infrared bands (AIBs) observed in the mid infrared spectrum are attributed to Polycyclic Aromatic Hydrocarbons (PAHs). We observe the NGC 7023-North West (NW) PDR in the mid-infrared (10 - 19.5 micron) using the Infrared Spectrometer (IRS), on board Spitzer. Clear variations are observed in the spectra, most notably the ratio of the 11.0 to 11.2 micron bands, the peak position of the 11.2 and 12.0 micron bands, and the degree of asymmetry of the 11.2 micron band. The observed variations appear to change as a function of position within the PDR. We aim to explain these variations by a change in the abundances of the emitting components of the PDR. A Blind Signal Separation (BSS) method, i.e. a Non-Negative Matrix Factorization algorithm is applied to separate the observed spectrum into components. Using the NASA Ames PAH IR Spectroscopic Database, these extracted signals are fit. The observed signals alone were also fit using the database and these components are compared to the BSS components. Three component signals were extracted from the observation using BSS. We attribute the three signals to ionized PAHs, neutral PAHs, and Very Small Grains (VSGs). The fit of the BSS extracted spectra with the PAH database further confirms the attribution to ionized and neutral PAHs and provides confidence in both methods for producing reliable results. The 11.0 micron feature is attributed to PAH cations while the 11.2 micron band is attributed to neutral PAHs. The VSG signal shows a characteristically asymmetric broad feature at 11.3 micron with an extended red wing. By combining the NASA Ames PAH IR Spectroscopic Database fit with the BSS method, the independent results of each method can be confirmed and some limitations of each method are overcome.

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