DUST IN HIGH-REDSHIFT RADIO GALAXIES AND THE EARLY EVOLUTION OF SPHEROIDAL GALAXIES

Several lines of evidence suggest that early-type galaxies might have been very dusty during their initial evolutionary stages, characterize d by intense star formation activity. The radio selection has provided , by far, the richest samples of high-z galaxies, which are most likel y to be of early type; they may therefore yield crucial direct informa tion on the period when the bulk of stars were born. In order to inves tigate the role of dust in these phases, we have analysed recent obser vations of a number of high-z radio galaxies in the framework of a sel f-consistent scenario for the evolution of early-type galaxies. The av ailable data can be fully accounted for by 'opaque' models similar to that already used by Mazzei & De Zotti to fit the spectrum of the hype rluminous galaxy IRAS F10214 + 4724. However, there is still considera ble latitude for models. Good fits can be obtained with galactic ages ranging from 0.05 to 2 Gyr. Crucial constraints may be provided by gro und-based submillimetre (submm) measurements and by observations with the forthcoming Infrared Space Observatory (ISO).