Dark Halo Approach Research Articles

Non-Gaussian tails of cosmological density distribution function from dark halo approach

We present a simple model based on the dark halo approach which provides a useful way to understand key points that determine the shape of the non-Gaussian tails of the dark matter one-point probability distribution function (PDF). In particular, using scale-free models with a power-law profile of dark haloes, we derive a simple analytic expression for the one-point PDF. It is found that the shape of the PDF changes at a characteristic value of δ*, which is defined by the smoothed density of a halo with characteristic mass M* at the epoch. In cold dark matter models with top-hat smoothing filters, the characteristic smoothed density at the present time typically takes the value δ*≫ 1 for a small smoothing scale Rth∼ 1 h−1 Mpc and conversely δ*≪ 1 for a large smoothing scale Rth > 10 h−1 Mpc. In the range δ/δ* 1 basically follow the steep exponential tails of the halo mass function, which exhibit a strong sensitivity on both the outer slope of the halo profile and the initial power spectrum. Based on these results, a discussion on the PDF of galaxy distribution and application to weak lensing statistics are also presented.

Reliability of the Dark Matter Clustering in CosmologicalN‐Body Simulations on Scales below the Mean Separation Length of Particles

We critically examine the reliability of the dark matter clustering in high-resolution cosmological N-body simulations on scales below the mean separation length of particles. The particle discreteness effect imposes the two fundamental limitations on those scales: the lack of the initial fluctuation power and the finite mass resolution. We address this problem applying the dark halo approach and are able to discuss separately how those two limitations affect the dark matter clustering in N-body simulations at early epochs. We find that limitations of the dark matter clustering are primarily determined by the mass of particles. By a detailed comparison with three major cosmological simulations, we also find that in order to reproduce a proper amplitude of the dark matter clustering on small scales, halos with a characteristic nonlinear mass, MNL(z), defined by σR(MNL; z) = 1, must be resolved in the simulation. This leads to a critical redshift zcrit determined by MNL(zcrit) = nhalompart, where nhalo is the number of particles necessary to resolve the typical nonlinear mass halo (~10). We conclude that, at least as far as the two-point correlation functions are concerned, the dark matter clustering in high-resolution N-body simulations on scales below the mean particle separation is reliable down to the gravitational force resolution length only for z zcrit.