Super-Eddington accretion in high-redshift quasar hosts: Black-hole driven outflows, galaxy quenching, and the nature of little red dots

TL;DR

We address how super-Eddington MBH accretion influences the coevolution of high-redshift quasar hosts and observable JWST signatures. We use a high-resolution cosmological zoom-in simulation with MBH seeding, accretion across regimes, and multi-phase ISM treatment, followed by spectral post-processing with a realistic AGN/stellar emission model. Key findings show that MBH feedback is often directional and moderate, but a major outburst can open a central cavity causing a transient ~50 Myr quenching; LRD-like spectra can arise post-super-Eddington growth, and some JWST quiescent signatures may reflect short-lived AGN-driven phases. These results frame LRDs and JWST quenching as transient stages in early massive galaxies, highlight the importance of time-resolved interpretation of JWST data, and provide observable diagnostics of MBH–host coupling in the early universe.

Abstract

The advent of the James Webb Space Telescope has revolutionised our understanding of the high-redshift Universe through its detection of bright, massive galaxies up to $z\gtrsim 10$ and its identification of peculiar sources called `little red dots' (LRDs). The origin of both classes of objects remains uncertain but is likely linked to the formation and early growth of the first massive black holes (MBHs), which may be more easily explained by invoking phases of super-Eddington accretion. In this study, we used a state-of-the-art zoom-in cosmological simulation of a quasar host to investigate whether these objects could resemble any of the peculiar sources observed with JWST during their assembly. We find that the impact of MBH feedback on star formation is typically moderate, with outflows preferentially escaping perpendicular to the galactic disc. However, for approximately ten percent of the galaxy's lifetime, the system enters a distinct quenched phase following rapid MBH growth driven by super-Eddington accretion. This phase culminates in a powerful feedback event, during which the MBH jet and disc-driven winds interact directly with the galactic disc and carve out a central cavity. We also find that, during the history of the quasar host progenitor, the spectral properties of the system can resemble both LRDs and quenched galaxies, depending on the specific evolutionary stage considered. These findings suggest that both conditions may represent transient phases in the life cycle of high-redshift galaxies.

Figures (14)

• Figure 1: Evolution of different components of the target galaxy. The solid black line corresponds to the halo mass (up to the virial radius), the dash-dotted gold one to the mass in stars, the solid red line to the total gas mass, the dashed blue line to the atomic hydrogen (H) mass content, the dash-double-dotted green line to the molecular hydrogen (H$_2$) mass content, and, finally, the dashed purple line to the black hole mass, scaled up by three orders of magnitude for visualisation purposes. With the grey shaded areas, we highlight distinct phases during the MBH accretion history: (i) super-Eddington accretion phases in the range $8.6\lesssim z\lesssim 9.5$, and (ii) accretion around the Eddington limit at $z\lesssim 7.9$.
• Figure 2: Evolution of the SFR of the target galaxy (as a solid red line). The best fit of the evolution obtained from the CEERS cole23 - which explicitly excluded sources potentially contaminated by AGNs - and the GLASS calabro24 surveys are shown below $z \simeq 9$ as dot-dashed green and dashed turquoise lines, respectively. We also report the 1$\sigma$ scatter as shaded areas, following the same colour scheme. The dotted purple line corresponds instead to the best fit to the empirical model by Behroozi13.
• Figure 3: Evolution of the luminosity emitted both in the form of radiation and kinetic energy by the stellar component (dot-dashed red line and dotted green line, respectively) and by the MBH accretion process (dashed orange line and solid blue line, respectively).
• Figure 4: Gaseous and stellar column density maps in a $100$ co-moving kpc box around the target galaxy at $z \approx 9.7, 8.3, 7.9$ from left to right and from top to bottom. The middle panels show the disruption of the gaseous disc, which is absent in the stellar counterpart. The outward expanding bubble of less dense material, with its centre located at the same position of the central MBH, suggests a MBH-driven origin.
• Figure 5: Top panels: Inflow mass rates (first row) and average radial velocities (second row) for the molecular (left), atomic (middle), and ionised (right) gas phases. The solid green lines represent inflows at $20 \ \mathrm{kpc}$, the dashed orange lines at $2 \ \mathrm{kpc}$, and the dot-dashed blue lines at $0.2 \ \mathrm{kpc}$. Bottom panels: Same as above but for outflows.