QAUNTITATIVE STUDY OF MID-INFRARED SPECTRA AND MID-INFRARED HYDROCARBON BANDS OF EXTERNAL GALAXIES

我们分析了IRTS和ISO对银河系平面的观测数据，发现中红外有机带的谱带比并不随入射辐射场的强度而变化。这一结果表明，与模型预测相反，星际有机物是完全电离的。我们还在Carina的数据中发现了大约22微米的宽带特征。在超新星遗迹和外部星系中也检测到了类似的波段。我们认为：(1)22微米带载流子可能是在超新星爆发时形成的；(2)它可以作为近期恒星形成活动的一个指标；(3)它可能会影响宽带光度测量。基于外部星系的远红外光谱，我们发现气体密度随着活动的增加而增加，而远红外特性不随星系的形态而改变。对红外相机数据的分析表明：(1)对于大多数星系来说，7微米到15微米的中红外颜色是由星系核的颜色决定的；(2)对条状星系来说，颜色降低；但(3)有些星系在延伸区显示的比例很低，这表明中红外颜色表明星系中的活动是短暂的。对从中红外到远红外的光谱能量分布的研究进一步表明，如果我们使用银河系平面的经验光谱能量分布，则可以一致地解释银河面和外部星系的光谱能量分布。建立了包括中红外波段在内的中红外特性模型，实现了本课题的主要目标。

We have analyzed the data taken by IRTS and ISO for the Galactic plane and found that the mid-infrared organic bands do not change their band ratios with the strength of incident radiation field. This result indicates that the interstellar organics are fully ionized contrary to the model predictions. We also found a broad band feature around 22 micron in the Carina data. A similar band is also detected in a supernova remnant and in an external galaxy. We suggest that (1) the 22 micron band carriers may be formed in supernova explosion, (2) it can be used an index for recent star formation activities, and (3) it could affect wide-band photometry. Based on the far-infrared spectroscopy of external galaxies, we found that the gas density increases with the activity and that the far-infrared characteristics do not change with the galaxy morphology. Analysis of infrared camera data indicates that (1) the total 7 micron to 15 micron mid-infrared color is determined by the color of the nucleus for most galaxies, (2) the color decreases for barred galaxies, but (3) there are some galaxies which show low ratios in the extended region, suggesting that the mid-infrared color indicates short-lived activities in galaxies. Investigations of the spectral energy distribution (SED) from mid-infrared to far-infrared further suggest that the SED of the Galactic plane and external galaxies can be accounted for consistently if we use an empirical SED of the Galactic plane. We have established a model that accounts for the mid-infrared characteristics, including the mid-infrared bands, and have achieved the primary goal of this project.