Mass Function of Low Mass Dark Halos

Abstract

The mass function of dark halos in a Lambda-dominated cold dark matter (LambdaCDM) universe is investigated. 529 output files from five runs of N-body simulations are analyzed using the friends-of-friends cluster finding algorithm. All the runs use 512^3 particles in the box size of 35 h^{-1}Mpc to 140 h^{-1}Mpc. Mass of particles for 35 h^{-1} Mpc runs is 2.67 times 10^7 h^{-1} M_{solar}. Because of the high mass resolution of our simulations, the multiplicity function in the low-mass range, where the mass is well below the characteristic mass and $\nu = \delta_c / \sigma \lesssim 1.0$, is evaluated in the present work, and is well fitted by the functional form proposed by Sheth & Tormen (ST). However, the maximum value of the multiplicity function from our simulations at $\nu \sim 1$ is smaller, and its low mass tail is shallower when compared with the ST multiplicity function.