A critical mass for Pop III stars: dependence on Lyman-Werner radiation, baryon/dark-matter streaming, and redshift

In ΛCDM cosmology, Pop III stars are typically expected to form in dark matter minihalos of mass 10⁵ - 10⁶ M_⊙. A critical mass (M_crit) can be defined as the minimum halo mass which can host sufficient cold dense gas that can lead to the formation of the first stars. The presence of Lyman-Werner radiation that can dissociate molecular hydrogen and baryon-dark matter streaming can delay the formation of Pop III stars by increasing M_crit. Although the delays from both of these effects have been studied individually, their combined effect has not been investigated previously using numerical simulations. In this work, we aim to constrain M_crit as a function of F_LW, v_streaming, and z using cosmological simulations with a large sample of halos using the AMR code Enzo. This function would be particularly useful for semi-analytical and analytical models of early galaxy formation. For the case with no baryon-dark matter streaming and no LW radiation, we have measured the z dependence of M_crit and find that it differs from either scaling with the virial temperature or the virial mass of the halo, as sometimes assumed in the past. The redshift evolution of M_crit has been predicted in many analytical calculations, but not seen previously with numerical simulations with a large number of halos.