Mixing of primordial gas in Lyman break galaxies

Motivated by a recent interpretation of z similar to 3 objects, we examine processes that control the fraction of primor-dial (Z = 0) gas, and so primordial stars, in high star formation rate Lyman break galaxies (LBGs). A primordial fraction different from 1 or 0 requires microscopic diffusion catalyzed by a velocity field with a timescale comparable to the duration of star formation. The only process we found that satisfies this requirement for LBGs without fine-tuning is turbulence-enhanced mixing induced by exponential stretching and compressing of metal-rich ejecta. The time dependence of the primordial fraction for this model is calculated. We show that conclusions for all the models discussed here are virtually independent of the initial mass function ( IMF), including extremely top-heavy IMFs.