INTERNAL VELOCITY AND MASS DISTRIBUTIONS IN SIMULATED CLUSTERS OF GALAXIES FOR A VARIETY OF COSMOGONIC MODELS

The mass and velocity distributions in the outskirts (0.5-3.0 h(-1) Mp c) of simulated clusters of galaxies are examined for a suite of cosmo gonic models (two Omega(0) = 1 and two Omega 0 = 0.2 models) utilizing large-scale particle-mesh (PM) simulations (500(3) cells, 250(3) part icles and box size of 100 h(-1) Mpc, giving a nominal resolution of 0. 2 h(-1) Mpc with the true resolution similar to 0.5 h(-1) Mpc). Throug h a series of model computations, designed to isolate the different ef fects, we find that both Omega 0, and P-k (lambda less than or equal t o 16 h(-1) Mpc) are important to the mass distributions in clusters of galaxies. There is a correlation between power, P-k, and density prof iles of massive clusters; more power tends to point to the direction o f a stronger correlation between alpha and M(r < 1.5 h(-1) Mpc) (see e q. [1] for definitions); i.e., massive clusters being relatively exten ded and small mass clusters being relatively concentrated. A lower Ome ga(0) universe tends to produce relatively concentrated massive cluste rs and relatively extended small mass clusters compared to their count erparts in a higher Omega 0 model with the same power. Models with lit tle (initial) small-scale power, such as the HDM model, produce more e xtended mass distributions than the isothermal distribution for most o f the mass clusters. But the CDM models show mass distributions of mos t of the clusters more concentrated than the isothermal distribution. X-ray and gravitational lensing observations are beginning providing u seful information on the mass distribution in and around clusters; som e interesting constraints on Omega 0 and/or the (initial) power of the density fluctuations on scales lambda less than or equal to 16 h(-1) Mpc (where linear extrapolation is invalid) can be obtained when large r observational data sets, such as the Sloan Digital Sky Survey, becom e available. With regard to the velocity distribution, we find two int eresting points. First, in 0.5 < r < 3.0 h(-1) Mpc region, all four ve locity dispersions (one-dimensional [1D], radial, tangential, line-of- sight) show decreasing distributions as a function of clustercentric d istance in the three CDM models; but the HDM model shows just the oppo site: weakly increasing velocity dispersions outward. The CDM models c an reasonably fit the observed galaxy velocity dispersions in the Coma cluster of galaxies but the HDM model provides a poor fit. Second, we find that for the scales 0.5 < r < 3.0 h(-1) Mpc, the tangential velo city dispersion is always larger than the radial component by a factor of 1.2-1.6 in the CDM models and 1.3-2.0 in the HDM model. In all mod els the ratio of radial to tangential velocity dispersions is a decrea sing function from 0.5 h(-1) Mpc to 3.0 h(-1) Mpc for massive clusters (smaller mass clusters tend to show a minimum for that ratio around 1 .5-2.0 h(-1) Mpc in the CDM models). While the velocity dispersions am ong the three Cartesian directions are isotropic on average, a large s catter (40%) exists in all models. We also examine the infall issue in detail. Lower Omega 0 models are found to have larger turnaround radi us for a fixed-mass clump than high Omega 0 models; this conclusion is insensitive to P-k. But we find that the following relation (between the turnaround radius, R(ta), and the mass within R(ta), M(ta)), log(1 0) R(ta) = a + b log(10) M(ta) (a = -5.2 +/- 0.2, b = 0.40 +/- 0.02, R (ta) and M(ta) are in h(-1) Mpc and h(-1) M., respectively) holds for all the models (the uncertainties in a and b indicate the variations a mong models). In addition, the relation between the overdensity inside the turnaround radius, delta(ta), and M(ta) is fitted by log(10) delt a(ta) = c + d log(10) M(ta) (cf. Table 1 for values of c and d). We sh ow that the spherical top-hat collapse model in an Einstein-de Sitter universe, having delta(ta) = 9 pi(2)/16 = 5.55, gives a fair fit to re sults (similar to 4-10) of the nonlinear, nonspherical simulations per formed here. Lower Omega 0 models have considerably higher delta(ta) s imilar to 10-30, as expected. Finally, we find that the isothermal app roximation (cf. eq. [10]) appears to underestimate the true masses wit hin the Abell radius by 10%-30% with a scatter of similar to 50% aroun d the estimated mean (in the three hierarchical models).