2014MNRAS.439.1092T

The origins of the ∼ 109M_☉ quasar supermassive black holes (BHs) at redshifts z > 6 remain a theoretical puzzle. One possibility is that they grew from ∼ 105M_☉ BHs formed in the `direct collapse' of pristine, atomic-cooling (temperatures ≳ 8000K; PAC) gas that did not fragment to form ordinary stars due to a lack of molecular hydrogen and metals. We propose that baryonic streaming - the relic relative motion of gas with respect to dark matter from cosmological recombination - provides a natural mechanism for establishing the conditions necessary for direct collapse. This effect delays the formation of the first stars by inhibiting the infall of gas into dark matter haloes; streaming velocities more than twice the root-mean-square value could forestall star formation until halo virial temperatures ≳ 8000K. The resulting PAC gas can proceed to form massive BHs by any of the mechanisms proposed in the literature to induce direct collapse in the absence of an ultraviolet background. This scenario produces haloes containing PAC gas at a characteristic redshift z ∼ 30. It can explain the abundance of the most luminous quasars at z ~ 6, regardless of whether direct collapse occurs in nearly all or less than 1 per cent of PAC haloes.