Effect of Streaming Motion of Baryons Relative to Dark Matter on the Formation of the First Stars

We evaluate the effect of a supersonic relative velocity between the baryons and dark matter on the thermal and density evolution of the first gas clouds at z less than or similar to 50. Through a series of cosmological simulations, initialized at z(i) = 100 with a range of relative streaming velocities and minihalo Formation redshifts, we find that the typical streaming velocities will have little effect on the gas evolution. Once the collapse begins, the subsequent evolution of the gas will be nearly indistinguishable from the case of no streaming, and star Formation will still proceed in the same way, with no change in the characteristic Pop III stellar masses. Reionization is expected to be dominated by halo masses of greater than or similar to 10(8)M(circle dot), for which the effect of streaming should be negligible.