  The discovery of a population of young galaxies at an epoch when the universe
was about one tenth of its current age has shed new light on the question of
when and how galaxies formed. Within the context of popular models this is the
population of primeval galaxies that built themselves up to the size of
present--day galaxies through the process of repeated mergers. But the recent
detection of a large concentration of these primeval galaxies (Steidel et al.
1997) appears to be incompatible with hierarchical clustering models, which
generally predict that clusters of this size are fully formed later in time.
Here we use a combination of two powerful theoretical techniques
--semi-analytic modelling and N-body simulations-- to show that such large
concentrations should be quite common in a universe dominated by cold dark
matter, and that they are the progenitors of the rich galaxy clusters seen
today. We predict the clustering properties of primeval galaxies which should,
when compared with data that will be collected in the near future, test our
understanding of galaxy formation within the framework of a universe dominated
by cold dark matter.
