ar X iv : a st ro - p h / 00 09 12 1 v 1 7 S ep 2 00 0 High - Redshift Galaxies : The Far - Infrared and Sub - Millimeter View

Observations at long wavelengths, in the wide interval from a few to 1000 μm, are essential to study diffuse media in galaxies, including all kinds of atomic, ionic and molecular gases and dust grains. Hence they are particularly suited to investigate the early phases in galaxy evolution, when a very rich ISM is present in the forming systems. During the last few years a variety of observational campaigns in the far-IR/sub-mm, exploiting both ground-based and space instrumentation, have started to provide results of relevant cosmological impact. Most crucial among these have been the discovery of an intense diffuse background in the far-IR/sub-mm of extragalactic origin, and the deep explorations from space in the far-IR and with large millimetric telescopes on ground. These results challenge those obtained from optical-UV observations, by revealing luminous to very luminous phases in galaxy evolution at substantial redshifts, likely corresponding to violent events of star-formation in massive systems. This is bringing to significant refinements of the present schemes of galaxy formation, as far as the history of baryon transformations is concerned. To appear in the Proceedings of the XI CANARY ISLANDS WINTER SCHOOL OF ASTROPHYSICS on ”Galaxies at High Redshift”, F. Sanchez, I. Perez-Fournon, M. Balcells, F. Moreno-Insertis Eds., Cambridge University Press.