Abundance and clustering of C iv absorption systems in the SCDM, LCDM, and CHDM models

We have developed a method for calculating the two-point correlation function of nonlinearly evolved mass and collapsed halos in the Press-Schechter formalism. The nonlinear gravitational interaction is treated as the sum of various individual spherical top-hat clustering. Because no collapsed halo of mass M can exist in initial regions (or top-hat spheres) of mass less than M, the bias that massive halos have stronger correlation than the background mass can be naturally introduced. We apply this method to derive constraints on popular dark-matter models from the spatial number density and the correlation function of C IV absorption systems in QSO spectra. Considering C IV systems should be hosted by collapsed halos, one can obtain an upper limit to the threshold mass of the collapsed halos by requiring their number density to be larger than that of observed C IV systems. On the other hand, in order to explain the observed clustering of C IV systems, a lower limit to the threshold mass will be set for the hosting halos. We found that the standard cold dark matter (SCDM) model and the low-density flat universe with a cosmological constant Lambda(0) (LCDM) are consistent with the abundance and clustering of C IV systems. However, the two cold-plus-hot dark matter models (CHDMs) with the cosmological parameters (Omega(c) + Omega(b))/Omega(h) = 0.7/0.3 and 0.8/0.2, respectively, have difficulty passing the two tests simultaneously. In these models, in order to have enough collapsed halos to host C IV systems, the threshold mass of the halos cannot be greater than 10(11) M.. But in order to agree with the two-point correlation function on the scales of Delta upsilon similar to 300-1000 km s(-1), the threshold mass should be larger than 10(12) M..