A HYDRODYNAMIC TREATMENT OF THE TILTED COLD DARK-MATTER COSMOLOGICAL SCENARIO

The evolution of a Tilted Cold Dark Matter (TCDM) model containing bot h baryonic matter and dark matter has been computed using our standard hydrodynamic code coupled with a Particle-Mesh (PM) code to calculate the motion of collisionless particles. We adopt the parameters n = 0. 7, h = H-0/100 km s-1 Mpc-1 = 0.5, OMEGA = 1.0, and OMEGA(b) = 0.06 wi th amplitude of the perturbation spectrum fixed by the COBE DMR signal s on very large scales giving (deltaM/M)rms = sigma8 = 1/b = 0.5 in a 8 h-1 Mpc top hat sphere at z = 0. Three different boxes are simulated with box sizes of L = (64, 16, 4) h-1 Mpc, respectively, the smallest box providing good resolution but little valid information due to the absence of large-scale power. We use 128(3) approximately 10(6.3) bar yonic cells and an equal number of dark matter particles. In addition to the dark matter we follow separately six baryonic species (H, H+, H e, He+, He++, e -) with allowance for both (nonequilibrium) collisiona l and radiative ionization in every cell. The background radiation fie ld and radiation losses are also followed in detail with allowance mad e for bremsstrahlung and Compton and free-bound emission, as well as i onization losses and line emission. The mean final Zel'dovich-Sunyaev y parameter is estimated to be yBAR = (5.4 +/- 2.7) x 10(-7), below cu rrently attainable observations, with an rms fluctuation of approximat ely deltayBAR = (6.0 +/- 3.0) x 10(-7) on arcminute scales. This TCDM model can make about 6% of the observed soft X-ray background in the 0 .1-1.0 keV range. The model fails by a large factor to produce enough ionization either by shocks or radiation to satisfy the high-redshift Gunn-Peterson test. Addition of UV from stars in forming galaxies may remedy this problem. We also examine the properties of X-ray-emitting regions and the two-point correlation functions of the ''galaxies''-th e cooled, bound regions. The rate of galaxy formation peaks at a relat ively late epoch (z approximately 0.5). With regard to mass function, the smallest objects are stabilized against collapse by thermal energy : the mass-weighted mass spectrum peaks in the vicinity of m(b) = 10(9 .1) MD With a reasonable fit to the Schechter luminosity function if t he baryon mass to blue light ratio is approximately four. These hydrod ynamic simulations complement the pure N-body simulations, and illustr ate the interesting properties of the TCDM model. We show that a bias factor b = 2 required for the model to be consistent with COBE DMR sig nals is probably a natural outcome in our multiple component simulatio ns. Overall the model is more successful than standard biased CDM on l arge scales, but exacerbates the temporal problems of CDM with regard to very late formation of galaxies and of structure.