UCLA

It is well established in the local Universe that regions of high star-formation rate are dusty. As a result of this physical causal link, galaxies of increasing current star formation activity emit a larger proportion of their bolometric luminosity via dust absorption and re-radiation in the thermal mid- to far-infrared. Several new observations indicate that this trend continues back to earlier cosmic times, when star formation rates were very high, and a large fraction of the resulting UV power was reprocessed by dust into the infrared. For studying the more luminous, (and therefore more dusty) galaxies, infrared spectroscopy is crucial even at moderate redshifts. For the less dusty galaxies, we are still driven strongly to longer wavelengths as their redshifts increase from 5 to 10. On the observational side, infrared astronomy is about to start catching up with optical astronomy in sensitivity, spatial resolution and field-of-view. Therefore, long-wavelength observations will play the key role in our understanding of galaxy formation and evolution in the ``Immature Universe."