Connecting reionization to the local universe

Abstract

We present results of combined N-body and three-dimensional reionization calculations to determine the relationship between reionization history and local environment in a volume of 1 Gpc h -1 across and a resolution of about 1 Mpc. We achieve this by applying three-dimensional simulations of reionization, based on the extended Press-Schechter formalism, to the same initial conditions as the N-body simulations. We resolve about 2 × 10 6 halos of mass greater than ∼ 1012 M⊙ at z = 0, and determine the relationship between halo mass and reionization epoch for galaxies and clusters. For our fiducial reionization model, in which reionization begins at z ∼ 15 and ends by z ∼ 6, we find a strong bias for cluster-size halos to be in the regions that reionized first, at redshifts 10 < z < 15. Consequently, material in clusters was reionized within relatively small regions, on the order of a few Mpc, implying that all clusters in our calculation were reionized by their own progenitors. Milky Way mass halos were on average reionized later and by larger regions, with a distribution most similar to the global one, indicating that low-mass halos are nearly uncorrelated with reionization when only halo mass is taken as a prior. On average, most halos with mass less than 1013 M⊙ were reionized internally, while almost all halos with masses greater than 10 14 M⊙ were reionized by their own progenitors. We briefly discuss the implications of this work in light of the "missing satellites" problem and how this new approach may be extended further. © 2009. The American Astronomical Society. All rights reserved.