The impact of metallicity on the formation of pre-collapsing minihalos

Abstract

In this study we consider the pre-enrichment of minihalos, and study the impact of metallicity on pre-collapsing minihalos by using the cosmological, N-body simulation code Enzo. The metallicities that we consider are assumed to be the result of pre-enrichment by earlier star formation. In the simulations of 10⁻³ and 10⁻¹ Z_⊙ we see a big difference for the collapse of the minihalo. In the high metallicity case the minihalo is more compact compared to the low metallicity case and we reach higher densities due to the efficient cooling. Also in the high metallicity case the gas cools down to lower temperatures and we see cold, dense gas which indicates a multi-phase ISM. This leads us to think that there is a transition region between metallicities of 10⁻³ and 10₋₁ Z_⊙ which lowers the mass scale of the next generation of stars. Furthermore, because the gas cools more efficiently in the high metallicity case there is less pressure support against gravity and therefore we see higher velocities.