Among the potentially most important results of Cosmology in the last decade is the realization that the star formation rate at redshifts z > 1 may have been higher than at present, and that much of the light produced by stars at high redshift reaches us in the FIR, after having been reprocessed by dust. Most of the FIR radiation background may have been produced at high z, and reaches us in the submm spectral range. The recent detection of a galaxy at z = 6.4 in CO (Walter et al. 2003; submitted to Nature) indicates that a large fraction of the baryonic material was already converted into metals less than 1 Gyr after the Big Bang. Did the origin of galaxies occur in a bath of infrared light? Were the bursts of star formation that may have accompanied the episodes of galaxy birth associated with the formation of quasars and supermassive black holes?
In the late 1990s, the SCUBA bolometer array on the JCMT identified a population of high z, highly luminous and dusty galaxies as the main source of the FIR/submm radiation background. Painstakingly, more than one hundred such sources have been detected by the SCUBA surveys over the last few years, and for only a handful of them are redshifts known. Many of them are invisible at optical wavelengths. Little is known about the overall properties of these objects. If, as generally speculated, they resemble low z ultra luminous infrared galaxies, which have star formation rates orders of magnitude higher than normal galaxies like our own, their rest frame SED would peak near 100 µm — and the vast majority of their flux would be emitted in the FIR. As galaxies at increasing z are observed, their flux at a fixed restframe wavelength would decrease as the inverse square of their luminosity distance; however, in the observer's frame the peak of their SED moves into the submm regime, so that the flux remains roughly constant in the observed submm band. This is why an understanding of the star formation history of the Universe must necessarily tread through bservations in the submm wavelength range. It is also interesting to note that in the galaxies' rest frame, their nonthermal emission kicks in at a wavelength of about 2–3 mm. Thus, the "window of opportunity'' for observations of the dust emission of ULIRGs from the ground is favorable over the decade between 200 µm and 2000 µm, i. e., from the atmospheric cutoff to the onset of predominance of nonthermal processes.