Cosmological simulations of the effects of primordial molecules on the first generation of stars

Abstract

In this study I present new results based on the implementation of molecular cooling and primordial streaming velocities into the hydro-dynamical simulation code GASOLINE. I demonstrate that the inclusion of molecular cooling as a cooling branch in the primordial gas and the addition of a homogeneous streaming velocity in the initial velocity field, are both critical to the study of Pop III stars. Pop III stars have a profound impact on galaxy formation, completely altering the chemical composition and thermal evolution of the gas. Future observations with the SKA telescope are expected to reveal some of the signatures of primordial star formation and thus enable the comparison with the numerical predictions. Numerical simulations employed to model the evolution of the primordial gas are able to capture the dynamics wellenough to predict the formation times of Pop III stars. The present study confirms that H2 and HD are the most dominant coolants at high redshifts. The implementation of a homogeneous streaming velocity field, generated by the decoupling of gas and DM at the epoch of decoupling (z ~ 1100), delays the collapse of the gas at the centre of the DM haloes and thus delays Pop III star formation. The overall result of the implementation of molecular cooling and primordial streaming velocities is that they compensate each other to a certain degree, such that the formation times of the first stars remain roughly unchanged - accelerated by the inclusion of molecules and decelerated as a consequence of the primordial streaming velocities, but it is unclear whether these effects exactly compensate one another.