Outflows in super-Eddington quasars drive clumpy circumgalactic medium and extended H$α$ nebulae at $z \gtrsim 6$

Lucas Tortora, Tiago Costa, Debora Sijacki, Jake S. Bennett

First listed 2026-07-27 | Last updated 2026-07-23

Abstract

The discovery of gargantuan black holes with masses exceeding a billion solar masses at $z\gtrsim6$ suggests rapid black hole growth and significant energy input into their host galaxies in the early Universe. With JWST probing previously unseen phases of the interstellar (ISM) and circumgalactic (CGM) medium around $z > 6$ quasars, detailed theoretical studies can now be directly confronted with observations. We use zoom-in simulations of a massive protocluster at $z\sim6$, employing both the fiducial FABLE galaxy formation model and modifications that allow earlier black hole seeding and mildly super-Eddington accretion. The central quasar remains Compton-thick throughout most of its evolution, with the obscuration arising from the ISM of its compact host galaxy. The onset of sufficiently strong quasar feedback drives a 'blow-out' episode, clearing out escape channels for ionizing radiation and leaving the central engine unobscured. This leads to a complete transformation of the CGM, whereby powerful, metal-enriched outflows produce a population of cold, fast, neutral clumps, significantly increasing the covering fraction of neutral hydrogen in the host halo. Radiative transfer calculations performed with a new ray-tracing code show that the CGM responds to quasar activity through the formation of H$α$ nebulae, whose size and luminosity increase with the strength of quasar feedback and decrease with obscuration level. Enhanced early black hole growth thus fundamentally reshapes the ISM and CGM of $z\sim6$ quasars, leaving clear observable signatures in their obscuration, neutral hydrogen distribution, and extended H$α$ emission.

Short digest

Using zoom-in protocluster simulations with earlier black-hole seeding and mildly super-Eddington accretion, Tortora et al. follow how repeated quasar-feedback blow-outs alter the obscuration, outflowing gas, and CGM of a z~6 quasar. The super-Eddington model transitions from a compact-host, Compton-thick growth phase to an unobscured state, while metal-enriched feedback produces fast cold neutral clumps that raise the halo H I covering fraction by as much as 64% and can persist beyond the virial radius. Ray-tracing calculations predict that the cleared escape channels and restructured CGM generate more extended Hα nebulae, with size and luminosity increasing with feedback strength and declining central obscuration. The work ties early rapid SMBH growth to jointly testable signatures in quasar obscuration, neutral-gas geometry, and extended recombination-line emission.

Key figures to inspect

• Figure 2. This establishes the central obscuration history by comparing hydrogen columns from the three simulations and showing how AGN-driven blow-out cycles lower the central column density. It also documents the ray-tracing treatment used to quantify the Compton-thick-to-unobscured transition.
• Figure 6. This is the key physical diagnostic for the paper's cold-clump result: the super-Eddington run contains substantially more fast cold outflowing gas, linked to efficient cooling of the hot wind. Its redshift sequence connects the emerging multiphase outflow directly to the stronger cumulative feedback model.
• Figure 9. This figure makes the population-level CGM consequence quantitative, relating excess DLA-level H I covering fraction within 50 kpc to cumulative quasar-mode feedback energy. It shows that strong feedback can raise the covering fraction by up to 64% by transporting dense neutral clumps into the halo.
• Figure 12. This provides the clearest observational synthesis, contrasting obscured, transitional, and unobscured phases of the same super-Eddington quasar after a roughly 1 Myr illumination episode. It shows how feedback-cleared channels allow ionizing photons to reach CGM clumps and filaments, igniting extended Hα emission even when the source photon rate is lower.
• Figure 13. These surface-brightness profiles translate the simulated Hα morphology into an observational diagnostic by including viewing-angle variation, dust attenuation, NIRSpec IFU sensitivity, and comparison to the BEES sample. The flattening of the profile as the quasar becomes unobscured is a concise testable prediction of the feedback-driven scenario.