Accurate initial conditions in mixed Dark Matter--Baryon simulations

Abstract

We quantify the error in the results of mixed baryon--dark-matter hydrodynamic simulations, stemming from outdated approximations for the generation of initial conditions. The error at redshift 0 in contemporary large simulations, is of the order of few to ten percent in the power spectra of baryons and dark matter, and their combined total-matter power spectrum. After describing how to properly assign initial displacements and peculiar velocities to multiple species, we review several approximations: (1) {using the total-matter power spectrum to compute displacements and peculiar velocities of both fluids}, (2) scaling the linear redshift-zero power spectrum back to the initial power spectrum using the Newtonian growth factor ignoring homogeneous radiation, (3) using longitudinal-gauge velocities with synchronous-gauge densities, and (4) ignoring the phase-difference in the Fourier modes for the offset baryon grid, relative to the dark-matter grid. Three of these approximations do not take into account that dark matter and baryons experience a scale-dependent growth after photon decoupling, which results in directions of velocity which are not the same as their direction of displacement. We compare the outcome of hydrodynamic simulations with these four approximations to our reference simulation, all setup with the same random seed and simulated using Gadget-III.

10 pages, 5 figures

References in corpus (9)

• The EAGLE project: Simulating the evolution and assembly of galaxies and their environments
• Introducing the Illustris Project: Simulating the coevolution of dark and visible matter in the Universe
• The Effective Field Theory of Cosmological Large Scale Structures
• Nonlinear Evolution of Baryon Acoustic Oscillations
• The clustering of galaxies in the completed SDSS-III Baryon Oscillation Spectroscopic Survey: cosmological implications of the configuration-space clustering wedges
• Constraint on neutrino masses from SDSS-III/BOSS Ly$\alpha$ forest and other cosmological probes
• Calibrating the Baryon Oscillation Ruler for Matter and Halos
• Cosmological $N$-body simulations including radiation perturbations
• A Relativistic view on large scale N-body simulations

Cited by in corpus (3)

• SP(k) -- A hydrodynamical simulation-based model for the impact of baryon physics on the non-linear matter power spectrum
• Turbulence-induced deviation between baryonic field and dark matter field in the spatial distribution of the Universe
• Numerical Discreteness Errors in Multi-Species Cosmological N-body Simulations