The Critical Dark Matter Halo Mass for Population III Star Formation: Dependence on Lyman–Werner Radiation, Baryon-dark Matter Streaming Velocity, and Redshift

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Abstract A critical dark matter halo mass (M crit) for Population III stars can be defined as the typical minimum halo mass that hosts sufficient cold-dense gas required for the formation of the first stars. The presence of Lyman–Werner (UV) radiation, which can dissociate molecular hydrogen, and the baryon-dark matter streaming velocity both delay the formation of Population III stars by increasing M crit. In this work, we constrain M crit as a function of Lyman–Werner flux (including self-shielding), baryon-dark matter streaming, and redshift using cosmological simulations with a large sample of halos utilizing the adaptive mesh refinement code enzo. We provide a fit for M crit as a function of these quantities, which we expect to be particularly useful for semi-analytical models of early galaxy formation. In addition, we find (i) the measured redshift dependence of M crit in the absence of radiation or streaming is (1 + z)−1.58, consistent with a constant virial temperature; (ii) increasing the UV background increases M crit while steepening the redshift dependence, up to (1 + z)−5.7; (iii) baryon-dark matter streaming boosts M crit but flattens the dependence on redshift; (iv) the combination of the two effects is not simply multiplicative.