The formation of the first quasars: the black hole seeds, accretion, and feedback models

Supermassive black holes (SMBHs) of similar to 10(9) M-circle dot are generally believed to be the central engines of the luminous quasars observed at z greater than or similar to 6, but their astrophysical origin remains elusive. To investigate the formation of these distant quasars, we perform a suite of zoom-in simulations on a favourable halo, with a mass of similar to 10(13) M-circle dot at z = 6 and a history of multiple major mergers, ideal for BH growth. We test BH seeds of 10-10(6) M-circle dot, and various accretion and feedback models, including thin-disc and slim-disc accretion. We find that abundant gas supply and efficient angular momentum transport by gravitational torques are critical to BH accretion, and that the final BH mass depends strongly on the seed mass and radiative efficiency which in turn depends on feedback model. In our simulations, heavy seeds of greater than or similar to 10(4) M-circle dot can grow rapidly to SMBHs of 10(8)-10(9) M-circle dot by z similar to 6 in both thin and slim disc accretion models, provided that the duty cycle of near-Eddington accretion with an Eddington ratio lambda(Edd) greater than or similar to 0.6 is maintained at greater than or similar to 40 per cent. In particular, for a 10(5) M-circle dot seed, both our fiducial model and the supercritical accretion model with no spin produce bright quasars with SMBHs of similar to 10(9) M-circle dot at z similar to 7.5. On the other hand, the light seeds of less than or similar to 10(3) M-circle dot failed to grow to 10(8) M-circle dot by z similar to 6 in our simulations. We caution that the results are inconclusive due to limitations of our numerical methods and physical models, and we stress the need for further investigations on the growth of BH seeds with more advanced methods.

Automated summary

By conducting zoom-in simulations on black hole seeds in star systems, it is found that abundant gas supply and efficient angular momentum transport through gravitational torques are crucial for black hole accretion. The final black hole mass depends on the seed mass and radiative efficiency, and seeds with a mass of at least 10^4 solar masses can rapidly grow to become supermassive black holes in both thin and slim disc accretion models.