1203.4184 (Francisco-Shu Kitaura)

The Initial Conditions of the Universe from Constrained Simulations    [PDF]

Francisco-Shu Kitaura

I present a new approach to recover the initial conditions and the cosmic web structure underlying a galaxy distribution. The method is based on sampling Gaussian fields which are compatible with a galaxy distribution and a structure formation model. This is achieved by splitting the inversion problem into two Gibbs-sampling steps: the first being a Gaussianisation step transforming a distribution of point sources at Lagrangian positions -which are not a priori given- into a linear alias-free Gaussian field. This step is based on Hamiltonian sampling with a Gaussian-Poisson model. The second step consists on a matching procedure in which the set of matter tracers at the initial conditions is constrained on the galaxy distribution and the structure formation model we assume. For computational reasons we use second order Lagrangian Perturbation Theory.We demonstrate taking a semi-analytic halo-model based galaxy mock catalog that the recovered initial conditions are closely unbiased with respect to the actual ones from the corresponding N-body simulation down to scales of a few Mpc/h. The cross-correlation between them shows a substantial gain of information, being at k ~ 0.3 h/Mpc more than doubled. In addition the initial conditions are extremely well Gaussian distributed and the power-spectra follow the shape of the linear power-spectrum being very close to the actual one from the simulation down to scales of k ~ 1 h/Mpc.

View original: http://arxiv.org/abs/1203.4184