1210.7871 (M. A. Aragon-Calvo)

The MIP Ensemble Simulation: Local Ensemble Statistics in the Cosmic Web    [PDF]

M. A. Aragon-Calvo

Here we present a novel N-body simulation technique that allows us to compute ensemble statistics on a local basis, directly relating halo properties to their environment. This is achieved by the use of an ensemble simulation in which the otherwise independent realizations share the same fluctuations above a given cut-off scale. This produces a constrained ensemble where the LSS is common to all realizations while having an independent halo population. By generating a large number of semi-independent realizations we can effectively increase the local halo density by an arbitrary factor thus breaking the fundamental limit of the finite halo density (for a given halo mass range) determined by the halo mass function. This technique allows us to compute local ensemble statistics of the matter/halo distribution at a particular position in space, removing the intrinsic stochasticity in the halo formation process and directly relating halo properties to their environment. This is a major improvement over global descriptors of the matter/halo distribution which can not resolve local variations. We introduce the Multum In Parvo (MIP) constrained ensemble simulation consisting of 220 realizations of a 32 h^{-1} Mpc box with 256^3 particles each. We illustrate the potential of the technique presented here by computing the local mass function at several characteristic environments and along a path from the center of a void to its border. We can study for the first time the effect of local environment in the height, shape and characteristic mass of the halo mass function.

View original: http://arxiv.org/abs/1210.7871