THE SEEDS OF RICH GALAXY CLUSTERS IN THE UNIVERSE

The discovery(1) of a population of young galaxies at a redshift when the Universe was about a tenth of its current age has shed new light o n the question of when and how galaxies formed. Within the context of popular models(2), this is the population of primeval galaxies that bu ilt themselves up to the size of present-day galaxies through the proc ess of repeated mergers called hierarchical clustering. But the recent detection(3) of a large concentration of these primeval galaxies appe ars to be incompatible with hierarchical clustering models, which gene rally predict that clusters of this size are fully formed later in tim e, Here we use a combination of theoretical techniques-semi-analytic m odelling and n-body simulations-to show that such large concentrations should be quite common in a universe dominated by cold dark matter an d that they are the progenitors of the rich galaxy clusters seen today . We predict the clustering properties of primeval galaxies which shou ld, when compared with data that will be collected in the near future, test our current understanding of galaxy formation within the framewo rk of a universe dominated by cold dark matter.