Determine the origin of the extended velocity structure and AGN contribution

Determine whether the rising velocity gradient in the extended nebula of AEON-z5 is produced by gravitationally supported or corotating gas, an AGN-driven outflow accelerating into a lower-density environment, recycled inflow, or a starburst-driven wind, and establish whether an active galactic nucleus is present in the central region.

Background

The F444W grism data show distinct kinematic behavior in the compact core and extended nebula: the core has a broad, multi-peaked emission-line profile, while the extended nebula exhibits a predominantly one-sided velocity gradient whose centroid shifts redward with projected radius. The paper discusses four possible interpretations: gravitationally supported or corotating outer gas, an accelerating AGN-driven outflow, recycled inflow in a galactic-fountain cycle, and an extreme starburst-driven wind.

The available imaging, slitless-grism spectroscopy, and SED modeling do not uniquely determine the gas geometry or excitation source. The authors identify spatially resolved integral-field spectroscopy, an independent systemic-redshift measurement from cold gas, and a direct continuum-size measurement as necessary to distinguish among these scenarios and clarify the role of an AGN.

References

The overall scenario is not uniquely determined. Several interpretations remain for the rising velocity gradient at large radii, and for whether an AGN is present.

— AEON-z5: A Candidate AGN-driven Outflow Enriching the Circumgalactic Medium at $z\simeq5.23$  (2609.08264 - Wei et al., 8 Sep 2026) in Section 4.4, “Possible Scenarios”

The velocity field shows a coherent gradient across the emission (Fig.~\ref{fig:cgm}a, inset); whether it reflects rotation of an extended CGM gas reservoir, an interaction, or outflowing gas remains open for now \citep{Akins2022,Wong2022,Knudsen2025}.

— ALMA2040: The High-Redshift Circumgalactic Medium. Imaging the fueling and feedback of galaxies in the early universe  (2610.21776 - Butler et al., 15 Oct 2026) in Section “ALMA2040: Key science cases for the CGM and galactic winds,” subsection “Imaging of the Cool CGM around Normal Star-Forming Galaxies at z ≃ 4–8,” paragraph “A gravitationally lensed view with current ALMA”