Structure Formation with Cold plus Hot Dark Matter
Abstract
We report results from high-resolution particle-mesh (PM) N-body simulations of structure formation in an Ω = 1 cosmological model with a mixture of cold plus hot dark matter (C + HDM) having Ωcold = 0.6, Ων = 0.3, and Ωbaryon = 0.1. We present analytic fits to the C + HDM power spectra for both cold and hot (neutrino) components, which provide initial conditions for our nonlinear simulations. In order to sample the neutrino velocities adequately, these simulations included 6 times as many neutrino particles as cold particles. Our simulations boxes were 14, 50, and 200 Mpc cubes (with H0 = 50 km s-1 Mpc-1); we also did comparison simulations for cold dark matter (CDM) in a 50 Mpc box.
C + HDM with linear bias factor b = 1.5 is consistent both with the COBE data and with the galaxy correlations we calculate. We find the number of halos as a function of mass and redshift in our simulations; our results for both CDM and C + HDM are well fitted by a Press-Schechter model. The number density of galaxy-mass halos is smaller than for CDM, especially at redshift z > 2, but the numbers of cluster-mass halos are comparable. We also find that on galaxy scales the neutrino velocities and flatter power spectrum in C + HDM result in galaxy pairwise velocities that are in good agreement with the data, and about 30% smaller than in CDM with the same biasing factor. On scales of several tens of megaparsecs, the C + HDM streaming velocities are considerably larger than CDM. As a result, the "cosmic Mach number" in C + HDM is about a factor of 2 larger than in CDM, and probably in better agreement with observations. Thus C + HDM looks promising as a model of structure formation. The presence of a hot component requires the introduction of a single additional parameter beyond standard CDM the light neutrino mass or, equivalently, Ων -- and allows the model to fit essentially all the available cosmological data remarkably well. The τ neutrino is predicted to have a mass of about 7 eV, compatible with the MSW explanation of the solar neutrino data together with a long-popular particle physics model. We outline a number of additional tests to which the C + HDM model should be subjected.- Publication:
-
The Astrophysical Journal
- Pub Date:
- October 1993
- DOI:
- 10.1086/173210
- arXiv:
- arXiv:astro-ph/9305011
- Bibcode:
- 1993ApJ...416....1K
- Keywords:
-
- COSMOLOGY: DARK MATTER;
- COSMOLOGY: LARGE-SCALE STRUCTURE OF UNIVERSE;
- COSMOLOGY: THEORY;
- GALAXIES: CLUSTERING;
- GALAXIES: FORMATION;
- METHODS: NUMERICAL;
- Astrophysics
- E-Print:
- 33pp., 16+ figures not included (available by mail), SCIPP-92/52