The formation of massive black holes in z ∼ 30 dark matter haloes with large baryonic streaming velocities

• DOI: 10.1093/mnras/stu042
• Publication Date: 2014-02-05T04:21:28Z
• Authors: Takamitsu L. Tanaka; Miao Li
• Keywords: Cosmology and Nongalactic Astrophysics (astro-ph.CO); 13. Climate action; 0103 physical sciences; FOS: Physical sciences; 01 natural sciences; 7. Clean energy; Astrophysics - Cosmology and Nongalactic Astrophysics

10 pages, 4 figures, 1 table; accepted for publication in MNRAS. v2 matches accepted version. (Not to be confused with Tanaka, Li & Haiman 2013, arXiv 1309.2301, which investigated the effect of baryonic streaming on suppressing SMBH formation from Population III remnants.)<br/>The origins of the ~10^9 Msun quasar supermassive black holes (BHs) at redshifts z > 6 remain a theoretical puzzle. One possibility is that they grew from ~10^5 Msun BHs formed in the 'direct collapse' of pristine, atomic-cooling (temperatures T ~ 8000 K; 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 Tvir ~ 8000 K. 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 a 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.<br/>