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Early structure in ΛCDM




We use a novel technique to simulate the growth of one of the most massive progenitors of a supercluster region from redshift z∼ 80, when its mass was about 10 M, until the present day. Our nested sequence of N-body resimulations allows us to study in detail the structure both of the dark matter object itself and of its environment. Our effective resolution is optimal at redshifts of 49, 29, 12, 5 and 0 when the dominant object has mass 1.2 × 105, 5 × 107, 2 × 1010, 3 × 1012 and 8 × 1014 h−1 M, respectively, and contains ∼106 simulation particles within its virial radius. Extended Press–Schechter (EPS) theory correctly predicts both this rapid growth and the substantial overabundance of massive haloes we find at early times in regions surrounding the dominant object. Although the large-scale structure in these regions differs dramatically from a scaled version of its present-day counterpart, the internal structure of the dominant object is remarkably similar. Molecular hydrogen cooling could start as early as z∼ 49 in this object, while cooling by atomic hydrogen becomes effective at z∼ 39. If the first stars formed in haloes with virial temperature ∼2000 K, their comoving abundance at z= 49 should be similar to that of dwarf galaxies today, while their comoving correlation length should be ∼2.5 h−1 Mpc.