http://arxiv.org/abs/2201.11757
One of the most pressing questions in cosmology is how the black holes (BHs) inferred to power quasars at high redshift are able to grow to supermassive scales well within a billion years of the Big Bang. Here we show that sustained super-Eddington accretion can be achieved for BHs with Eddington fractions $f_{\rm Edd}$ $>$ 2/$\epsilon$, where $\epsilon$ is the efficiency with which radiation is generated in the accretion process. In this regime, the radiation carries too little momentum to halt the accretion flow and the infalling gas traps the radiation, carrying it into the BH. The BH growth then proceeds unimpeded until the gas supply in its vicinity is exhausted, in contrast to accretion at lower rates which is limited by the radiation generated in the accretion process. The large gas supply available in massive high redshift quasar host galaxies may be readily be accreted onto seed BHs via this supply-limited mode of accretion, providing an explanation for how such supermassive BHs are assembled in the early universe. This sustained super-Eddington growth may also explain the short lifetimes inferred for the H II regions surrounding high redshift quasars, if the bulk of the BH growth occurs without the radiation generated in the process escaping to ionize the intergalactic medium. It also implies that a population of obscured rapidly growing BHs may be difficult to detect, perhaps explaining why so few quasars with Eddington fractions higher than a few have been observed. Finally, this simple condition for sustained super-Eddington growth can easily be implemented in cosmological simulations which can be used to assess how often and in which environments it occurs.
J. Johnson and P. Sanderbeck
Mon, 31 Jan 22
53/55
Comments: 5 pages; 2 figures; 10 equations; to be submitted to ApJ
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