Bias and Conditional Mass Function of Nonspherical Dark Halos

Nonspherical collapse is modelled, under the Zeldovich approximation, by sixdimensional random walks of the initial deformation tensor field. The collapse boundary adopted here is a slightly-modified version of that proposed by Chiueh and Lee (2001). Not only the mass function agrees with the fitting formula of Sheth and Tormen (1999), but the bias function and conditional mass function constructed by this model are also found to agree reasonably well with the simulation results of Jing (1998) and Somerville et al. (2000), respectively. In particular, by introducing a small mass gap, we find a fitting formula for the conditional mass function, which works well even at small time intervals between parent and progenitor halos during the merging history. Subject headings: galaxies:clusters:general cosmology:theory large-scale structure of universe Email: [email protected] Email: [email protected] Email: [email protected]