Simulation of Primordial Object Formation

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 first 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 find that postvirialization properties are insensitive to the initial abundance of H2. Our main objective was to determine the minimum mass [MSG(z)] of 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 find that we can do so with a baryonic particle mass resolution of 40 M☉. We have performed cosmological simulations of primordial objects, and find that the object's mass and redshift at which they become self-gravitating agree well with the MSG(z) results from the top-hat simulations. Once a critical H2 fractional abundance of ~5 × 10-4 has formed in an object, the cooling time 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.