The PAH Emission Characteristics of the Reflection Nebula NGC 2023
The PAH Emission Characteristics of the Reflection Nebula NGC 2023
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反射星云 NGC 2023 的 PAH 发射特征
DOI：
10.3847/1538-4357/836/2/198
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发表时间：
2017
期刊：
影响因子：
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通讯作者：
M. Wolfire
中科院分区：
文献类型：
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作者：
E. Peeters;C. Bauschlicher;L. Allamandola;A. Tielens;A. Ricca;M. Wolfire
我们提供了反射星云NGC 2023的5-20 μm光谱图，这些光谱图是用斯皮策太空望远镜上的红外光谱仪SL和SH模式获得的，它们显示了叠加在尘埃连续体上的多环芳烃（PAHs）、C60和H2的发射。我们发现，多环芳烃的发射带相互关联，并表现出不同的空间分布，揭示了一个空间序列与照明星星的距离。我们探索了6.2、7.7和8.6 μm PAH谱带的不同形态，发现NGC 2023中至少有两种空间上不同的组分对7-9 μm PAH的发射做出了贡献。我们报告说，PAH功能的行为独立的基础高原。我们目前的光谱紧凑，椭圆形的多环芳烃的大小范围从C66到C210，计算确定使用密度泛函理论，我们调查的趋势，作为PAH的大小，电荷和几何形状的函数的频带位置和相对强度。根据NASA艾姆斯多环芳烃数据库，对7-9 μm组分进行了谱带归属和相对强度分析。我们将平台发射分配给非常小的颗粒，可能来自PAH簇的贡献，并确定了7-9 μm发射中可能源自这些结构的成分。基于这些分配和观测到的空间序列，我们讨论了在NGC 2023光离解区蒸发流中，随着多环芳烃越来越多地暴露于中心星星的辐射场，星际多环芳烃族的光化学演化.
We present 5–20 μm spectral maps of the reflection nebula NGC 2023 obtained with the Infrared Spectrograph SL and SH modes on board the Spitzer Space Telescope, which reveal emission from polycyclic aromatic hydrocarbons (PAHs), C60, and H2 superposed on a dust continuum. We show that several PAH emission bands correlate with each other and exhibit distinct spatial distributions that reveal a spatial sequence with distance from the illuminating star. We explore the distinct morphology of the 6.2, 7.7, and 8.6 μm PAH bands and find that at least two spatially distinct components contribute to the 7–9 μm PAH emission in NGC 2023. We report that the PAH features behave independently of the underlying plateaus. We present spectra of compact, oval PAHs ranging in size from C66 to C210, determined computationally using density functional theory, and we investigate trends in the band positions and relative intensities as a function of PAH size, charge, and geometry. Based on the NASA Ames PAH database, we discuss the 7–9 μm components in terms of band assignments and relative intensities. We assign the plateau emission to very small grains with possible contributions from PAH clusters and identify components in the 7–9 μm emission that likely originate in these structures. Based on the assignments and the observed spatial sequence, we discuss the photochemical evolution of the interstellar PAH family as the PAHs are more and more exposed to the radiation field of the central star in the evaporative flows associated with the Photo-Dissociation Regions in NGC 2023.