Mid-Infrared Characteristics of Star-Forming Complexes in Irregular Galaxies
Mid-Infrared Characteristics of Star-Forming Complexes in Irregular Galaxies
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不规则星系中恒星形成复合体的中红外特征
DOI：
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发表时间：
2007
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通讯作者：
M. Kaufman
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文献类型：
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作者：
D. Hunter;M. Kaufman
本文给出了斯皮策空间望远镜红外光谱仪10-37 μm高分辨率光谱图，显示了5个不规则星系的11个恒星形成区。我们测量或上限的星云精细结构线，分子线从温暖的H2，和各种多环芳烃（PAH）的功能，以探测恒星辐射场的硬度，星云的电子密度，和物理环境中，多环芳烃被加热。星云有类似的激发，对应于一个中型O型星星，电子密度在大多数区域都很低。除了两个星云外，所有星云都检测到了多环芳烃，在氧丰度较高的星系中，相对于恒星的多环芳烃排放量或Hα排放量往往较高。人口的多环芳烃似乎是不同的IM星系比它是在螺旋。我们模拟了一个星云中温暖的H2的辐射，得到温度为800 K，中性气体密度≥105 cm-3，远紫外辐射场G 0 ≥ 103。整个星云的激发变化很小，但PAH 11.2 μm的发射在整个地图上变化了3-4倍。恒星形成区域的局部H I或H II环境的差异导致Im星系之间星云精细结构线发射的中红外比率只有轻微的差异。然而，多环芳烃排放量的变化更为明显。
We present Spitzer Space Telescope Infrared Spectrograph 10-37 μm high-resolution spectral maps of 11 star-forming regions in five irregular galaxies. We measure or place upper limits on nebular fine-structure lines, molecular lines from warm H2, and various polycyclic aromatic hydrocarbon (PAH) features in order to probe the hardness of the stellar radiation field, the electron density of the nebulae, and the physical environment in which PAHs are being heated. The nebulae have similar excitations, corresponding to a midtype O star, and electron densities are low in most regions. PAHs were detected in all but two nebulae, and PAH emission relative to stars or Hα emission tends to be higher in galaxies with higher oxygen abundances. The population of PAHs appears to be different in Im galaxies than it is in spirals. We model emission from warm H2 in one nebula to obtain a temperature of 800 K, a neutral gas density ≥105 cm-3, and a far-UV radiation field of G0 ≥ 103. Variations in excitation across the nebulae are small, but the PAH 11.2 μm emission varies by factors of 3-4 across the maps. Differences in the local H I or H II environment of star-forming regions result in only mild differences in mid-IR ratios of nebular fine-structure line emission among Im galaxies. Variations in PAH emission, however, are more evident.