Efficient Highly Subsonic Turbulent Dynamo and Growth of Primordial Magnetic Fields.

We present the first study on the amplification of magnetic fields by the turbulent dynamo in the highly subsonic regime, with Mach numbers ranging from 10^{-3} to 0.4. We find that for the lower Mach numbers the saturation efficiency of the dynamo (E_{mag}/E_{kin})_{sat} increases as the Mach number decreases. Even in the case when injection of energy is purely through longitudinal forcing modes, (E_{mag}/E_{kin})_{sat}≳10^{-2} at a Mach number of 10^{-3}. We apply our results to magnetic field amplification in the early Universe and predict that a turbulent dynamo can amplify primordial magnetic fields to ≳10^{-16}  G on scales up to 0.1 pc and ≳10^{-13}  G on scales up to 100 pc. This produces fields compatible with lower limits of the intergalactic magnetic field inferred from blazar γ-ray observations.