Inception of a first quasar at cosmic dawn

Earliest quasars at the cosmic dawn are powered by mass accretion on to supermassive black holes of a billion solar masses. Massive black hole (MBH) seeds forming through the direct collapse mechanism are considered the most promising candidates but how do they grow and coevolve with their host galaxies at early cosmic times remains unknown. We here present results from a cosmological radiation hydrodynamical simulation including self-consistent modelling of both Population III (Pop III) and Population II (Pop II) star formation, their radiative and supernova feedback in the host galaxy along with X-ray feedback from an accreting MBH of 105 M⊙ in a halo of 2 × 109 M⊙ from z = 26 down to z = 16. Our results show that energy deposition from X-rays in the proximity of MBH suppresses Pop III star formation for about 12 Myr while at the same time these X-rays catalyse H2 formation that leads to the formation of a Pop III star cluster of 500 M⊙ in the close vicinity of the MBH. We find that mode of star formation for Pop III is episodic and bursty due to the clumpy accretion, while for Pop II it is continuous. The stellar mass of the host galaxy at z ∼16 is 2 × 107 M⊙ with a star formation rate of ∼ 0.1-1 M⊙ yr-1. In total, the MBH accretes 1.5 × 106 M⊙ during 120 Myr with the mean accretion rate of ∼ 0.01 M⊙ yr-1 corresponding to an average Eddington fraction of 50 per cent.