| 總結: | Soon after the IRAS mission, the first ever mission in exploring the Infrared world from space, it was realised that there exists a great number of galaxy populations that are extremely luminous at infrared wavelengths. Yet, their optical output was significantly smaller when compared to their infrared one. The enormous amounts of dust present in these galaxies is of course the reason for the different appearence of these galaxies at different wavelengths. And although optical spectroscopy is generally a useful tool, it can not provide much inside on these galactic nuclei as their centers suffer high extinctions. However, infrared spectroscopy although difficult to be performed from the ground, is the ideal tool for probing the obscured nuclei of galaxies. The Infrared Space Observatory (ISO) provides the best opportunity to probe these obscured nuclei, and even more, promises to open up our view of the infrared world.
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