Simulation of Primordial Object Formation

Abstract

We have included the chemical rate network responsible for the formation of molecular hydrogen in the N-body hydrodynamic code, HYDRA, in order to study the formation of the Ðrst cosmological objects at redshifts between 10 and 50. We have tested our implementation of the chemical and cooling processes by comparing N-body top-hat simulations with theoretical predictions from a semianalytic model and found them to be in good agreement. We Ðnd that postvirialization properties are insensitive to the initial abundance of Our main objective was to determine the minimum mass of H 2 . [ M SG (z)] perturbations that could become self-gravitating (a prerequisite for star formation), and the redshift at which this occurred. We have developed a robust indicator for detecting the presence of a self-gravitating cloud in our simulations, and Ðnd that we can do so with a baryonic particle mass resolution of 40 M _ . We have performed cosmological simulations of primordial objects, and Ðnd that the objectÏs mass and redshift at which they become self-gravitating agree well with the results from the top-hat simula-M SG (z) tions. Once a critical fractional abundance of D5 ] 10~4 has formed in an object, the cooling time H 2 drops below the dynamical time at the center of the cloud and the gas free falls in the dark matter potential wells, becoming self-gravitating a dynamical time later.