Proto-clusters in the Λcdm Universe

We compare the highly clustered populations of very high redshift galaxies with proto-clusters identified numerically in a standard ΛCDM universe (Ω0 = 0.3, λ0 = 0.7) simulation. We evolve 2563 dark matter particles in a comoving box of side 150h−1Mpc. By the present day there are 63 cluster sized objects of mass in excess of 10hM⊙ in this box. We trace these clusters back to higher redshift finding that their progenitors at z = 4–5 are extended regions of typically 20–40 Mpc (comoving) in size, with dark halos of mass in excess of 10hM⊙ and are overdense by typically 1.3–13 times the cosmological mean density. Comparison with the observation of Lyα emitting (LAEs) galaxies at z = 4.86 and at z = 4.1 indicates that the observed excess clustering is consistent with that expected for a proto-cluster region if LAEs typically correspond to massive dark halos of more than 10hM⊙. We give a brief discussion on the relation between high redshift concentration of massive dark halos and present day rich clusters of galaxies. Subject headings: galaxies:clusters:general – cosmology:theory – methods:numerical