Fourier imaging of non-linear structure formation

We perform a Fourier space decomposition of the dynamics of non-linear cosmological structure formation in LCDM models. From N-body simulations involving only cold dark matter we calculate 3-dimensional non-linear density, velocity divergence and vorticity Fourier realizations, and use these to calculate the fully non-linear mode coupling integrals in the corresponding fluid equations. Our approach allows for a reconstruction of the amount of mode coupling between any two wavenumbers as a function of redshift. With our Fourier decomposition method we identify the transfer of power from larger to smaller scales, the stable clustering regime, the scale where vorticity becomes important, and the suppression of the non-linear divergence power spectrum as compared to linear theory. Our results can be used to improve and calibrate semi-analytical structure formation models.Comment: 22 pages, 8 figures, matches published versio

Cosmological N-body simulations with generic hot dark matter

We have calculated the non-linear effects of generic fermionic and bosonic hot dark matter components in cosmological N-body simulations. For sub-eV masses, the non-linear power spectrum suppression caused by thermal free-streaming resembles the one seen for massive neutrinos, whereas for masses larger than 1eV, the non-linear relative suppression of power is smaller than in linear theory. We furthermore find that in the non-linear regime, one can map fermionic to bosonic models by performing a simple transformation.Comment: 19 pages, 9 figure

Resolving Cosmic Neutrino Structure: A Hybrid Neutrino N-body Scheme

We present the first simulation capable of resolving the structure of neutrino clustering on Mpc scales. The method combines grid- and particle-based methods and achieves very good accuracy on both small and large scales, while keeping CPU consumption under control. Such simulations are not only ideal for calculating the non-linear matter power spectrum but also particularly relevant for studies of how neutrinos cluster in galaxy- or cluster-sized halos. We perform the largest neutrino N-body simulation to date, effectively containing 10 different neutrino hot dark matter components with different thermal properties.Comment: 13 pages, 6 figure

The Effect of Thermal Neutrino Motion on the Non-linear Cosmological Matter Power Spectrum

We have performed detailed studies of non-linear structure formation in cosmological models with light neutrinos. For the first time the effect of neutrino thermal velocities has been included in a consistent way, and the effect on the matter power spectrum is found to be significant. The effect is large enough to be measured in future, high precision surveys. Additionally, we provide a simple but accurate analytic expression for the suppression of fluctuation power due to massive neutrinos. Finally, we describe a simple and fast method for including the effect of massive neutrinos in large-scale N-body simulations which is accurate at the 1% level for \sum m_nu < 0.15 eV.Comment: 17 pages, 7 figures. Minimal changes, matches JCAP versio

Neutrinos in Non-linear Structure Formation - The Effect on Halo Properties

We use N-body simulations to find the effect of neutrino masses on halo properties, and investigate how the density profiles of both the neutrino and the dark matter components change as a function of the neutrino mass. We compare our neutrino density profiles with results from the N-one-body method and find good agreement. We also show and explain why the Tremaine-Gunn bound for the neutrinos is not saturated. Finally we study how the halo mass function changes as a function of the neutrino mass and compare our results with the Sheth-Tormen semi-analytic formulae. Our results are important for surveys which aim at probing cosmological parameters using clusters, as well as future experiments aiming at measuring the cosmic neutrino background directly.Comment: 20 pages, 8 figure