X-Ray Gas Density Profile of Clusters of Galaxies from the Universal Dark Matter Halo

The X-ray cluster gas density distribution in hydrostatic equilibrium is computed from the universal density profile of the dark matter halo proposed by Navarro, Frenk, & White in two recent studies. If one assumes the isothermality, the resulting distribution is well approximated by the conventional β-model. We predict the core radius r_c, the β-parameter, and the X-ray luminosity of clusters as a function of the temperature T_X of clusters in some representative cosmological models and compare them with observations and results of numerical simulations. The predicted size of r_c is a factor of 3-10 smaller than the average of observed values. If both the universal density profile and the hydrostatic equilibrium are reasonable approximation to the truth, then this suggests either that the previous X-ray observations systematically overestimated the core radius of gas densities in clusters of galaxies or that some important physical mechanisms, which significantly increase the core radius, are still missing.