OBSERVATIONAL STUDIES ON THE NEAR-INFRARED UNIDENTIFIED EMISSION BANDS IN GALACTIC H ii REGIONS
OBSERVATIONAL STUDIES ON THE NEAR-INFRARED UNIDENTIFIED EMISSION BANDS IN GALACTIC H ii REGIONS
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DOI：
10.1088/0004-637x/784/1/53
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发表时间：
2014-01
期刊：
影响因子：
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通讯作者：
Tamami I. Mori;T. Onaka;I. Sakon;D. Ishihara;T. Shimonishi;R. Ohsawa;Aaron C Bell
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文献类型：
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作者：
Tamami I. Mori;T. Onaka;I. Sakon;D. Ishihara;T. Shimonishi;R. Ohsawa;Aaron C Bell
利用大量的银河系H ii区和类H ii区天体的近红外光谱（2.5-5.4 μm），我们对天文多环芳烃（PAH）特征进行了系统的研究。使用AKARI卫星上的红外照相机观测了36个物体，这是主任时间方案的一部分。除了众所周知的3.3-3.6 μm特征外，大多数光谱在5.22 μm处显示出相对较弱的发射特征，具有足够的信噪比，我们将其确定为PAH 5.25 μm带（先前报道）。通过仔细分析，我们发现5.25 μm谱带与3.3 μm处的芳烃特征和3.4-3.6 μm处的脂肪烃特征有很好的相关性。目前的结果为我们提供了令人信服的证据，天文5.25 μm波段与C-H振动，如以前的研究所建议的，并显示其潜在的探测PAH的尺寸分布。分析还表明，多环芳烃的电离分数I3.4-3.6 μm/I3.3 μm随3.7 μm连续谱强度与3.3 μm连续谱强度之比I3.7 μm/I3.3 μm而减小。I9 μm/I18 μm的中红外色也随4.05 μm处的氢复合线Brα与3.3 μm带的比值IBrα/I3.3 μm急剧下降。这些事实表明，电离气体内部或边界处可能存在粉尘处理。
Using a large collection of near-infrared spectra (2.5–5.4 μm) of Galactic H ii regions and H ii region-like objects, we perform a systematic investigation of astronomical polycyclic aromatic hydrocarbon (PAH) features. Thirty-six objects were observed using the infrared camera on board the AKARI satellite as a part of a director's time program. In addition to the well known 3.3–3.6 μm features, most spectra show a relatively weak emission feature at 5.22 μm with sufficient signal-to-noise ratios, which we identify as the PAH 5.25 μm band (previously reported). By careful analysis, we find good correlations between the 5.25 μm band and both the aromatic hydrocarbon feature at 3.3 μm and the aliphatic hydrocarbon features at around 3.4–3.6 μm. The present results give us convincing evidence that the astronomical 5.25 μm band is associated with C–H vibrations, as suggested by previous studies, and show its potential to probe the PAH size distribution. The analysis also shows that the aliphatic-to-aromatic ratio of I3.4–3.6 μm/I3.3 μm decreases against the ratio of the 3.7 μm continuum intensity to the 3.3 μm band, Icont, 3.7 μm/I3.3 μm, which is an indicator of the ionization fraction of PAHs. The midinfrared color of I9 μm/I18 μm also declines steeply against the ratio of the hydrogen recombination line Brα at 4.05 μm to the 3.3 μm band, IBrα/I3.3 μm. These facts indicate possible dust processing inside or at the boundary of ionized gas.