Extreme Enrichment at Cosmic Dawn: Three FeII-Strong Quasars at z > 6 from the JWST Aether survey

Anniek J. Gloudemans, Emanuele Paolo Farina, Roberto Decarli, Klaudia Protušová, Fabrizio Arrigoni Battaia, Eduardo Bañados, Aaron J. Barth, Silvia Belladitta, Manuela Bischetti, Hyunseop Choi, Dominika Ďurovčíková, Anna-Christina Eilers, Simona Gallerani, Thales A. Gutcke, Luca Ighina, Brian C. Lemaux, Federica Loiacono, Yoshiki Matsuoka, Chiara Mazzucchelli, Silvia Onorato, Hyewon Suh, Fabian Walter, Feige Wang, Julien Wolf, Jinyi Yang

First listed 2026-09-18 | Last updated 2026-09-16

Abstract

We present three outliers on the quasar main sequence at z>6, as revealed by JWST/NIRSpec IFU observations from the Aether survey, a program targeting ~200 quasars at cosmic dawn. The quasars, J0216-5226, J0320-3521, and J1429+5447, exhibit exceptionally strong FeII emission and weak H$β$ and [OIII] lines, indicating rapid chemical enrichment within the first Gyr of cosmic history. Their FeII strengths ($R_{\rm{FeII},\lambda4570} \equiv \rm{EW}_{\rm{FeII}}/\rm{EW}_{\rm{H}β}$) range between ~2.5-3.6, placing them among the top ~3% of SDSS quasars at ($0\lesssim z\lesssim 1$). The H$α$ emission lines of J0216-5226 and J1429+5447 imply black hole masses of $\sim1-7\times10^9$ M$_{\odot}$ with $λ_{\rm{Edd}}\sim0.1-0.6$, comparable to typical high-z quasars, although virial black hole masses may be systematically overestimated in strong FeII emitters. In contrast, J0320-3521 hosts a lower mass black hole of $\sim0.2-2\times10^9$ M$_{\odot}$, suggesting possible super-Eddington rate accretion with $λ_{\rm{Edd}}$~0.5-6.0. The IFU data of J0320-3521 reveal a distinct emission-line region at a projected distance of ~1.5 kpc, consistent with either an interacting companion or ionized gas associated to the quasar. We further identify a complex environment around J1429+5447, including two candidate companion galaxies or extended ionized gas structures. These quasars with bright emission-line regions, J0320-3521 and J1429+5447, are radio-loud sources, while J0216-5226 remains undetected in radio ($R_{5\rm{GHz,} \,3σ}\lesssim4$). Together, these results confirm previous findings that highly enriched, rapidly growing black holes were already in place at cosmic dawn. Despite the small sample size, our results further highlight the diversity in environment and radio-jet properties among quasars that otherwise share the same extreme region of the quasar fundamental plane.

Short digest

Using JWST/NIRSpec IFU spectroscopy from the roughly 200-quasar Aether survey, this paper identifies J0216-5226, J0320-3521, and J1429+5447 as extreme z>6 outliers with very strong optical Fe II and weak Hβ and [O III]. Their R_FeII,λ4570≈2.5–3.6 places them in the top ∼3% of low-redshift SDSS quasars and makes them the most Fe II-strong high-redshift quasars yet observed, supporting rapid broad-line-region enrichment within the first Gyr. Hα-based estimates indicate otherwise typical massive, moderately accreting black holes in J0216-5226 and J1429+5447, while J0320-3521 may host a lower-mass, potentially super-Eddington accretor; resolved line-emitting structures around the latter two radio-loud quasars additionally expose diverse companion-galaxy or ionized-gas environments. The interpretation of the virial masses warrants caution because strong Fe II emitters may have systematically overestimated single-epoch mass estimates.

Key figures to inspect

• Figure 1. The NIRSpec IFU spectral fits directly establish the paper's defining evidence: unusually prominent Fe II emission together with weak Hβ and [O III] in all three z>6 quasars.
• Figure 3. This is the key population-context figure, placing the three Aether objects on the Hβ-width versus Fe II-strength Eigenvector 1 plane and showing that they occupy the extreme high-R_FeII tail relative to SDSS, other high-redshift quasars, and the full Aether sample.
• Figure 4. The quasar-subtracted Hβ, [O III], and Hα maps provide the central resolved-environment result, revealing the eastern emission-line region near J0320-3521 and the multiple structures around J1429+5447.
• Figure 8. The broad-band radio SED of J1429+5447 anchors the radio-loudness aspect of the interpretation and tests physically motivated spectral models for this Fe II-strong quasar with a complex environment.
• Figure 9. The alternative Fe II-template fits make the principal spectral-modeling systematic visible: the inferred Fe II equivalent widths and R_FeII values depend on whether the Mrk 493 or I Zw 1 template is adopted.