GALAXY FORMATION AT HIGH REDSHIFTS

SENSITIVE optical surveys have revealed(1) a large population of 'fain t blue galaxies', which are believed to be young galaxies observed clo se to their time of formation(2). But there has been considerable unce rtainty regarding the epochs at which these galaxies are observed, owi ng to the difficulties inherent in determining spectroscopic redshifts for very faint objects. Here, by modelling the numbers and colours of galaxies at the faintest detection limits, we show that the faint blu e galaxies are likely to lie at high redshift (z approximate to 2). Th is conclusion holds regardless of whether the Universe is assumed to b e open of at the critical density (flat). In an open universe, the dat a are consistent with galaxy models in which star formation rates deca y exponentially with decreasing redshift, whereas the assumption of a flat universe requires the addition of a population of galaxies which are seen only at high redshift.