WERE SMALL GALAXIES ONCE THE DOMINANT COSMOLOGICAL POPULATION

DEEP sky surveys have turned up unexpectedly large numbers of faint blue galaxies 1,2-three to five times more than would be estimated by extrapolation from the present galaxy population assuming no evolution. Unless distances to these faint galaxies are known, it is difficult to distinguish between luminosity evolution (in which case, galaxies in the past were systematically brighter) and density evolution (as, for example, if modern galaxies are the results of mergers of earlier ones). We have obtained redshifts and K magnitudes for a small but complete sample of 22 galaxies with B magnitude down to 24. In the luminosity range B = 23-24, the B-band galaxy counts are dominated by a population of small blue galaxies at z almost-equal-to 0.25, which may collectively contain as much baryonic matter as the normal galaxies. It is possible either that these earlier galaxies have undergone merging 3 to create the present galaxy population, or that they represent a quite different galactic population which has now faded or disappeared 4. Either possibility has considerable implications for our understanding of galaxy formation.