On the rapid growth of SMBHs in high-z galaxies: the aftermath of Population III.1 stars

Abstract: The vast amount of energy released by active galactic nuclei (AGN) is increasingly recognized as a key driver of evolution not only in massive galaxies and clusters, but also in low-mass dwarf galaxies. Despite this, their role in the early stages of galaxy formation and in self-regulating the rapid growth of the first and abundant supermassive black holes (SMBHs) remains poorly understood. Through new high-resolution zoom-in cosmological simulations, we follow the co-evolution of $10^5 M_\odot$ black hole seeds with their host galaxy. The simulated suite progressively spans physics ranging from no AGN feedback and Eddington-limited thermal feedback, to more complex setups including non-Eddington-limited thermal, kinetic and radiative feedback. Across all our models, we find that black hole seeds efficiently reach masses of $\sim10^7 M_\odot$ by z=8. Although they exhibit notably different mass growth histories, these latter seem unimpeded by the presence of AGN feedback. The simulation including radiative feedback is the most distinct, with super-Eddington episodes driving fast and mass-loaded gas outflows (exceeding 2500 km $s^{-1}$) up to $\sim$50 kpc, along with minor stellar mass suppression in the host galaxy. Our measurements are in broad agreement with moderate luminosity quasars recently observed by JWST, producing overmassive black holes, dynamical masses of $\sim10^{9.5} M_\odot$, and high, though short-lived, Eddington fraction accretion rates. These results advocate for a scenario where AGN feedback allows for rapid SMBH growth during the reionisation era, while driving winds that extend deep into the intergalactic medium - shaping host galaxies as well as more distant surroundings.