Connecting Reionization to the Local Universe
Abstract
We present results of combined Nbody and threedimensional 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 threedimensional simulations of reionization, based on the extended PressSchechter formalism, to the same initial conditions as the Nbody simulations. We resolve about 2 × 10^{6} halos of mass greater than ~10^{12} M _{sun} 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 clustersize 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 lowmass halos are nearly uncorrelated with reionization when only halo mass is taken as a prior. On average, most halos with mass less than 10^{13} M _{sun} were reionized internally, while almost all halos with masses greater than 10^{14} M _{sun} 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.
 Publication:

The Astrophysical Journal
 Pub Date:
 October 2009
 DOI:
 10.1088/0004637X/703/2/L167
 arXiv:
 arXiv:0812.3405
 Bibcode:
 2009ApJ...703L.167A
 Keywords:

 cosmology: theory;
 galaxies: formation;
 intergalactic medium;
 Astrophysics
 EPrint:
 4 pages, 5 figures, submitted to ApJ Letters, comments welcome. See http://www.slac.stanford.edu/~malvarez/ReionLocal for high resolution figures and animations