1,802 research outputs found
Dynamics of the baryonic component in hierarchical clustering universes
I present self-consistent 3-D simulations of the formation of virialized systems containing both gas and dark matter in a flat universe. A fully Lagrangian code based on the Smoothed Particle Hydrodynamics technique and a tree data structure has been used to evolve regions of comoving radius 2-3 Mpc. Tidal effects are included by coarse-sampling the density of the outer regions up to a radius approx. 20 Mpc. Initial conditions are set at high redshift (z greater than 7) using a standard Cold Dark Matter perturbation spectrum and a baryon mass fraction of 10 percent (omega(sub b) = 0.1). Simulations in which the gas evolves either adiabatically or radiates energy at a rate determined locally by its cooling function were performed. This allows us to investigate with the same set of simulations the importance of radiative losses in the formation of galaxies and the equilibrium structure of virialized systems where cooling is very inefficient. In the absence of radiative losses, the simulations can be rescaled to the density and radius typical of galaxy clusters. A summary of the main results is presented
Substructure in CDM Halos and the Heating of Stellar Disks
Numerical simulations have revealed the presence of long-lived substructure
in Cold Dark Matter (CDM) halos. These surviving cores of past merger and
accretion events vastly outnumber the known satellites of the Milky Way. This
finding has prompted suggestions that substructure in cold dark matter (CDM)
halos may be incompatible with observation and in conflict with the presence of
thin, dynamically fragile stellar disks. N-body simulations of a
disk/bulge/halo model of the Milky Way that includes several hundred dark
matter satellites with masses, densities and orbits derived from
high-resolution cosmological CDM simulations indicate that substructure plays
only a minor dynamical role in the heating of the disk. This is because the
orbits of satellites seldom take them near the disk, where their tidal effects
are greatest. We conclude that substructure might not preclude virialized CDM
halos from being acceptable hosts of thin stellar disks like that of the Milky
Way.Comment: Presented at the Yale Symposium "The Shape of Galaxies and their
Halos", ed. P.Nataraja
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