The observed interstellar extinction is reviewed briefly. A dust model consisting of amorphous silicate grains + carbonaceous grains (including PAHs) can successfully reproduce the observed extinction on different sightlines given appropriate size distributions. The model grains, exposed to interstellar starlight, will radiate in the infrared and far-infrared. The expected emission can be calculated from the physical properties of the grains. Grains in the SMC differ substantially from Milky Way dust in their extinction properties, and the calculated infrared emission spectra also differ. Recent observations of infrared emission from the Sb galaxy NGC 7331 are compared to the emission calculated for the amorphous silicate + carbonaceous grains dust model, using the size distributions adopted previously for modeling the dust in the local diffuse interstellar medium of the Milky Way. With appropriate choice of illuminating radiation field, the model reproduces the observed infrared emission, with the exception of a newly-discovered broad emission feature at 17.1μm. The 17.1μm feature, with FWHM = 0.96μm, carries approximately 3 times as much power as the 16.4μm PAH feature.
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机译：简要审查了观察到的星际灭绝。由非晶硅酸盐+碳质颗粒（包括PAH）组成的粉尘模型可以成功地再现在鉴于适当的尺寸分布的不同视线上的观察到的灭绝。暴露于星际星光的模型晶粒将在红外线和远红外辐射。预期的发射可以根据晶粒的物理性质计算。 SMC中的谷物在其消光特性中基本上不同于银河系灰尘，并且计算出的红外发射光谱也有所不同。将来自Sb Galaxy NGC 7331的红外发射的近期观察结果与针对无定形硅酸盐+碳质晶粒粉尘模型计算的发射进行比较，使用先前采用的尺寸分布用于对银河系的局部漫射间隙介质中的粉尘进行建模。与照明辐射场的适当的选择，该模型再现所观察到的红外发射，与17.1μm一个新发现的宽发射特征的例外。为17.1μm的特点，fwhm =0.96μm，带有大约3倍的电源，如16.4μmpah特征。
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