Aether-SHELLQs: JWST integral-field spectroscopy of candidate obscured quasars at z ~ 6

Yoshiki Matsuoka, Roberto Decarli, Emanuele Paolo Farina, Anniek J. Gloudemans, Eduardo Bañados, Fabrizio Arrigoni Battaia, Anna-Christina Eilers, Chiara Mazzucchelli, Michael A. Strauss, Hyewon Suh, Maxime Trebitsch, Fabian Walter, Feige Wang, Kentaro Aoki, Junya Arita

First listed 2026-06-10 | Last updated 2026-06-08

Abstract

We present James Webb Space Telescope (JWST) NIRSpec integral field unit (IFU) observations of six galaxies at $z \sim 6$, obtained as part of the Aether project (General Observers program 5645). The targets were originally identified by the Subaru High-$z$ Exploration of Low-Luminosity Quasars (SHELLQs) survey, as candidate obscured quasars with luminous ($\gtrsim10^{43}$ erg s$^{-1}$) but narrow ($\lesssim500$ km s$^{-1}$) Ly$α$ emission. Two objects exhibit a broad component in their Balmer lines (FWHM $>3000$ km s$^{-1}$), indicating the presence of active galactic nuclei (AGNs), while the remaining four show similar profiles in permitted and forbidden lines. Combining these data with similar SHELLQs objects reported previously, we find that the presence of broad lines is strongly correlated with Ly$α$ luminosity ($L_{\rm Lyα}$); the inferred AGN fraction is $>$77 % and $<$15 % above and below $L_{\rm Lyα} =10^{44}$ erg s$^{-1}$, respectively. Dust-extinction corrections inferred from the Balmer decrement would imply unrealistically high Ly$α$ luminosities, suggesting that the line-emitting gas consists of multiple zones. The IFU data reveal diverse spatial structures. The AGN hosts are compact, whereas the other galaxies show extended ionized gas on scales up to 10 kpc and star formation rates of 60 - 600 $M_\odot$ yr$^{-1}$. One of the extended objects exhibits a signature of rotation, while most of the others show little ordered kinematics, with velocity widths (FWHM) up to 200 - 300 km s$^{-1}$. These objects populate the intermediate luminosity regime between classical luminous quasars and the low-luminosity AGNs discovered by JWST, including Little Red Dots, potentially linking the two populations.

Short digest

JWST/NIRSpec IFU spectroscopy of six z ~ 6 Aether-SHELLQs galaxies shows that two host clear broad Balmer components with FWHM > 3000 km s^-1, while the other four have similar permitted and forbidden-line profiles and more extended ionized gas. When combined with earlier SHELLQs follow-up, the key result is that broad-line AGN incidence rises sharply with Lyα luminosity, with an inferred AGN fraction >77% above L_Lyα = 10^44 erg s^-1 and <15% below that threshold. The Balmer decrement does not support a simple one-zone dust correction, because it would imply implausibly luminous Lyα emission, favoring a multi-zone line-emitting medium instead. Spatially, the broad-line AGN hosts are compact, whereas the non-broad-line systems extend to ~10 kpc, show star-formation rates of 60-600 M_sun yr^-1, and mostly modest 200-300 km s^-1 kinematics, placing this sample in the intermediate regime that may connect classical quasars to JWST low-luminosity AGN and Little Red Dots.

Key figures to inspect

• Figure 2. This is the cleanest figure for the paper’s AGN identification, because it shows the line-profile decomposition around Hβ+[O III] and Hα+[N II] and makes clear which objects require broad Balmer components versus narrow-only fits. Readers can directly see that the central classification hinges on modeled Balmer-line structure rather than on Lyα selection alone.
• Figure 4. This is the conclusion-driving synthesis figure. It ties the present IFU sample to the earlier SHELLQs JWST sample, shows how broad-line detections track Lyα luminosity, and also visualizes the tension between Balmer-decrement dust corrections and the observed Lyα output, which motivates the multi-zone interpretation.
• Figure 5. This figure is the best population-context panel because it places the observed sources in the full SHELLQs M1450-Lyα plane and marks which JWST-observed systems do and do not show broad lines. It clarifies the sample definition, the intermediate-luminosity regime the paper is targeting, and why these objects matter as a bridge between classical quasars and fainter JWST-selected AGN.
• Figure 6. These IFU maps capture one of the paper’s main empirical results: compact hosts for the broad-line AGN candidates versus extended [O III] and Hα emission in the other systems on scales up to about 10 kpc. This figure is the most effective way to show that the sample is morphologically diverse and that several objects are not dominated by a purely compact nuclear component.
• Figure 7. This figure carries the kinematic interpretation by mapping [O III] flux, velocity, and velocity width across the six galaxies. It shows the single object with a rotational signature and the broader result that most extended systems lack strong ordered motion and instead have comparatively modest line widths, which is important for interpreting the ionized gas as extended and dynamically varied rather than uniformly quasar-like.