Simulations and Measurements of Warm Dark Matter Free-Streaming and Mass

Abstract

We compare simulated galaxy distributions in the cold Λ CDM and warm Λ WDM dark matter models. The ΛWDM model adds one parameter to the Λ CDM model, namely the cut-off wavenumber k fs of linear density perturbations. The challenge is to measure k fs . This study focuses on “smoothing lengths” π / k fs in the range from 12 Mpc to 1 Mpc. The simulations reveal two distinct galaxy populations at any given redshift z: hierarchical galaxies that form bottom up starting at the transition mas M fs , and stripped down galaxies that lose mass to neighboring galaxies during their formation, are near larger galaxies, often have filamentary distributions, and seldom fill voids. We compare simulations with observations, and present four independent measurements of k fs , and the mass m h of dark matter particles, based on the redshift of first galaxies, galaxy mass distributions, and rotation curves of spiral galaxies.