活动星系核和星暴星系中的多环芳烃和发射线比率
Polycyclic Aromatic Hydrocarbon and Emission Line Ratios in Active Galactic Nuclei and Starburst Galaxies
摘要：
我们研究了多环芳烃（PAH）带，离子发射线，和中红外连续光谱的性质，在一个样本的171个发射线星系从文献加上15个新的活动星系核（AGN）斯皮策光谱。连续谱的形状在较长的波长下急剧上升，并且可以与T=150- 300 K的暖黑体分布拟合。最亮的PAH光谱带（6.2，7.7，8.6，11.3和12.7 $μ$ m）和[Si II] 34.8 $μ$ m，[Ar II] 6.9，[S III] 18.7和33.4的禁止发射线在所有的星爆中被检测到，在80%的Seyfert~2中。仅考虑7.7 $μ$ m、11.3 $μ$ m和12.7 $μ$ m处的PAH条带，我们发现它们存在于约80%的Seyfert 1中，而只有一半的这种类型的活性显示6.2 $μ$ m和8.6 PAH条带。中性和电离多环芳烃的观测强度比（6.2/7.7 x 11.3/7.7）与理论强度比进行了比较，表明活动星系核比SB星系具有更高的电离分数和更大的多环芳烃（> 180个碳原子）。电离带（7.7）和中性PAH带（8.6和11.3）之间的比率分布在不同的范围内的活动星系核和SB星系，这表明这些比率可能取决于电离分数，以及对辐射场的硬度。随着[Ne III]15.5/[Ne II]的增加，7.7和11.3带之间的比率几乎是恒定的，这表明电离到中性PAH带的分数不依赖于辐射场的硬度。两种PAH特征的等效宽度与[Ne III]/[Ne II]的关系相同，表明PAH无论是发射电离带（7.7）还是中性带（11.3），都可能随着辐射场硬度的增加而被破坏。
英文摘要：
We study the Polycyclic Aromatic Hydrocarbons (PAH) bands, ionic emission lines, and Mid-infrared continuum properties, in a sample of 171 emission line galaxies taken from literature plus 15 new active galactic nuclei (AGN) Spitzer spectra. The continuum shape steeply rises for longer wavelengths and can be fitted with a warm blackbody distribution of T=150-300K. The brightest PAH spectral bands (6.2, 7.7, 8.6, 11.3, and 12.7$μ$m) and the forbidden emission lines of [Si II] 34.8$μ$m, [Ar II] 6.9, [S III] 18.7 and 33.4 were detected in all the Starbursts and in ~80% of the Seyfert~2. Taking under consideration only the PAH bands at 7.7$μ$m, 11.3$μ$m, and 12.7$μ$m we find they are present in ~80% of the Seyfert 1, while only half of this type of activity show the 6.2$μ$m and 8.6 PAH bands. The observed intensities ratios for neutral and ionized PAHs (6.2/7.7 x 11.3/7.7) were compared to theoretical intensity ratios, showing that AGNs have higher ionization fraction and larger PAH (> 180 carbon atoms) than SB galaxies. The ratio between the ionized (7.7) and the neutral PAH bands (8.6 and 11.3) are distributed over different ranges for AGNs and SB galaxies, suggesting that these ratios could depend on the ionization fraction, as well as on the hardness of the radiation field. The ratio between the 7.7 and 11.3 bands is nearly constant with the increase of [Ne III]15.5/[Ne II], indicating that the fraction of ionized to neutral PAH bands does not depend on the hardness of the radiation field. The equivalent width of both PAH features show the same dependence with [Ne III]/[Ne II], suggesting that the PAH, emitting either ionized (7.7) or neutral (11.3) bands, may be destroyed with the increase of the hardness of the radiation field.
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