Supersonic Turbulence in Primordial Halos: a Comparison with and without the Stream Velocity

Abstract Turbulence plays a critical role in regulating star formation in molecular clouds and is also observed in simulations of primordial halos that host Population III (Pop III) stars. The relative velocity between baryons and dark matter at the time of recombination is thought to be a source of turbulence in the early Universe. In this paper, we study how this stream velocity affects the turbulence inside primordial halos using high-resolution cosmological simulations across the redshift range of z = 30 to z = 20. We find that at a fixed redshift, the stream velocity enhances turbulence in low-mass halos ( M ≲ 10 6 M ⊙ ) and suppresses it for high-mass halos ( M ≳ 10 6 M ⊙ ). The enhancement in low-mass halos likely arises from residual kinetic energy introduced by the stream velocity, while the suppression in high-mass halos likely arises from a reduction in accretion-driven turbulence. This mass-dependent modulation of turbulence suggests that the initial conditions inside primordial halos are altered in the presence of the stream velocity, potentially influencing their fragmentation and the resulting star formation.