Inception of a first quasar at cosmic dawn

TL;DR

This study uses cosmological radiation hydrodynamical simulations to explore how early supermassive black holes and their host galaxies grow and evolve, revealing episodic star formation and the impact of X-ray feedback at cosmic dawn.

Contribution

It provides the first detailed simulation of early black hole growth and galaxy co-evolution including self-consistent Pop III and Pop II star formation and feedback mechanisms.

Findings

X-ray feedback suppresses Pop III star formation for 12 Myr.

X-rays catalyze H2 formation, enabling Pop III star cluster formation.

Black hole accretes 1.5 million solar masses over 120 Myr.

Abstract

Earliest quasars at the cosmic dawn are powered by mass accretion onto supermassive black holes of a billion solar masses. Massive black hole seeds forming through the direct collapse mechanism are considered the most promising candidates but how do they grow and co-evolve with their host galaxies at early cosmic times remains unknown. We here present results from a cosmological radiation hydrodynamical simulation including self-consistent modeling of both Pop III and Pop II star formation, their radiative and supernova feedback in the host galaxy along with X-ray feedback from an accreting massive black hole (MBH) of $\rm 10^5 ~M_{\odot}$ in a halo of $\rm 2 \times 10^9~M_{\odot}$ 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 catalyze $\rm H_2$ formation which leads to the formation of a Pop III star cluster of 500 $\rm M_{\odot}$ 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 $z \sim 16$ is $\rm 2 \times 10^7~M_{\odot}$ with a star formation rate (SFR) of $\rm \sim 0.1-1~M_{\odot}/yr$. In total, the MBH accretes $\rm 1.5 \times 10^6~M_{\odot}$ during 120 Myr with the mean accretion rate of $\rm \sim 0.01~M_{\odot}/yr$ corresponding to an average Eddington fraction of 50\%.