Shedding the envelope: JWST reveals a kiloparsec-scale [OIII]-weak Balmer shell around a z=7.64 quasar

TL;DR

Using JWST/NIRSpec IFU, the paper resolves nuclear and circumnuclear gas around the $z=7.6423$ quasar J0313$-$1806, finding a remarkably weak nuclear [O III] and a kiloparsec-scale H$\beta$ shell with no [O III] emission. Photoionization modeling shows that collisional de-excitation in a dense, clumpy shell or sub-solar metallicity can explain the extended [O III] deficit, implying a fossil outflow from a recent blowout and suggesting episodic, obscured growth of the black hole. The results connect WLQ-like UV/optical properties to a dense ISM environment and shed light on how early quasar feedback and ISM states can imprint on spectral properties across cosmic time. Collectively, the findings imply that dense, clumpy gas can regulate line emission while allowing intermittent feedback signatures to persist as fossil remnants around some of the earliest SMBHs.

Abstract

Luminous quasars at the redshift frontier z>7 serve as stringent probes of super-massive black hole formation and they are thought to undergo much of their growth obscured by dense gas and dust in their host galaxies. Fully characterizing the symbiotic evolution of SMBHs and hosts requires rest-frame optical observations that span spatial scales from the broad-line region to the ISM and CGM. JWST now provides the necessary spatially resolved spectroscopy to do so. But the physical conditions that regulate the interplay between SMBHs and their hosts at the highest redshifts, especially the nature of early feedback phases, remain unclear. We present JWST/NIRSpec IFU observations of J0313$-$1806 at z=7.64, the most distant luminous quasar known. From the restframe optical spectrum of the unresolved quasar, we derive a black hole mass of $M_\mathrm{BH}=(1.63 \pm 0.10)\times10^9 M_\odot$ based on H$β$ and an Eddington rate of $λ=L/L_\mathrm{Edd}=0.80\pm 0.05$, consistent with previous MgII-based estimates. J0313-1806 exhibits no detectable [O III] emission on nuclear scales. Most remarkably, we detect an ionized gas shell extending out to $\sim 1.8$ kpc traced by H$β$ emission that also lacks any significant [O III], with a $3σ$ upper limit on the [O III]$ λ$5007 to H$β$ flux ratio of $\log_{10} \left( F(\mathrm{[OIII]})/F(\mathrm{H}β)\right)=-1.15$. Through photoionization modelling, we demonstrate that the extended emission is consistent with a thin, clumpy outflowing shell where [OIII] is collisionally de-excited by dense gas. We interpret this structure as a fossil remnant of a recent blowout phase, providing evidence for episodic feedback cycles in one of the earliest quasars. These findings suggest that dense ISM phases may play a crucial role in shaping the spectral properties of quasars accross cosmic time.

Figures (15)

• Figure 1: Extracted quasar spectrum within a 035 aperture centred on the spaxel with the highest integrated flux. The observed spectrum, shown in black, is well fit by the PyQSOFit model, shown in orange. Broad H$\beta$ and H$\gamma$ are modelled using three and two broad Gaussian components (pink lines, individual Gaussians are shown in purple) with FWHM$>1200$ km/s, and one Gaussian component with FWHM$<1200$ km/s to trace narrow components (green line). The [O III] $\lambda\lambda$4959,5007 emission lines are modelled with one broad and one narrow component. No narrow [O III] $\lambda\lambda$4959,5007 components are detected, while a strong contribution from Fe ii emission (blue line) is evident park22. The lower panel shows fit residuals.
• Figure 2: PSF model. Left: Spectral comparison between the quasar and PSF star used to derive the PSF scaling factor. The extracted 1D spectra from the quasar (black) and PSF star (blue) were obtained using a circular aperture with radius 0 35. The PSF spectrum is scaled down by a factor of 500 for visual comparison. While the PSF star shows a smooth stellar continuum, the quasar exhibits a prominent broad H$\beta$ emission line and strong Fe ii features. The wavelength-dependent scaling factor $S(\lambda)$ computed as the ratio between the quasar and PSF spectra is shown in green. The scaling factor is smoothed with a Gaussian kernel of width $\sigma = 5$ pix before being applied slice by slice to the aligned PSF cube. Right: Median radial profiles extracted from the quasar cube (black dashed), the raw PSF star cube (orange) and the PSF star cube, corrected with the wavelength-dependent scaling factor (blue). The radial profiles are measured from the brightest pixel in white light of each cube. The colour-shaded areas correspond to the median absolute deviations of the quasar radial profile (grey) and the scaled PSF star cube (blue).
• Figure 3: PSF subtraction procedure for J0313--1806. Left: Integrated white-light image of the reduced cube centered on J0313--1806. The blue cross marks the position of the unresolved quasar. Centre: Integrated and scaled cube of the PSF calibration star TYC 5875-488-1, aligned and scaled to match the quasar emission. The orange cross marks the position of the unresolved star. Right: Residual white-light image of J0313--1806 after PSF subtraction, revealing extended emission components after removal of the unresolved quasar core. We highlight three regions of interest: A) A bright core near the quasar, B) a near-elliptical diffuse region just north-east of the quasar and C) a distinct foreground elliptical source to the south-west of the quasar. This work focuses on the central region A). For all maps, pixels with negative integrated flux were masked.
• Figure 4: Kinematic moment maps of H$\beta$ around J0313-1806 and bandwidth-matched continuum. Gaussian spatial smoothing over 2.5 pixel kernel was applied (at 005/pix scale). First panel: Flux map of $3\sigma$ detected H$\beta$ (57 spaxels). These are highlighted by the red contour. We define this distribution as H$\beta$ shell. Adjunct spaxels in 8-connectivity to these detection spaxels with at least S/N$_\mathrm{H\beta}> 1.5$ are also shown. The flux in the line peaks close to the quasar location, consistent with a central ionizing source. Second panel: Velocity offset map as traced by the the $v_{50}$ parameter. A clear velocity gradient is observed along the shell, indicating expansion or rotation of the structure. Spaxels with extreme velocities ($\mid v_{50} \mid >400 \, \mathrm{km\, s^{-1}}$) are marked with green contours. Third panel: Velocity dispersion, $\sigma$. Patches of large dispersions (>600 $\mathrm{km/s}$) are observed at the edges and to the south-east of the structure, potentially indicating highly turbulent gas motion. Fourth panel: Continuum map constructed by integrating the fitted continuum model over a line-free spectral window with bandwidth matched to that of H$\beta$. While elevated continuum emission overlaps spatially the with the H$\beta$ shell, the absence of brightened nuclear morphology in the map following the H$\beta$ flux confirms that the observed H$\beta$ structure is not driven by background variations or continuum residuals. The continuum map shows a clear flux peak offset to the north from the quasar position. This component does not trace the shell-like H$\beta$ morphology and lacks any associated kinematic structure. We therefore interpret it as artifact from imperfect fitting in imperfectly PSF-subtracted spaxels, rather than extended stellar or nebular continuum emission.
• Figure 5: Upper panel: Mean spectrum of the Balmer shell. This spectrum was extracted from 57 spaxels with at least $3\sigma$ H$\beta$ detections. The line (green dashed line), the continuum (orange dashed line), and the full (red line) models are from our q3dfit analysis. The fitted, redshifted [O III] $\lambda$5007 and continuum emissions are consistent with noise. Middle panel: Zoom in spectra of the H$\gamma$ and H$\beta$ regions. Lower panels: Mean spectra of blueshifted ($v_{50} < -25 \,\mathrm{km\,s^{-1}}$, left) and redshifted ($v_{50} > 25 \,\mathrm{km\,s^{-1}}$, right) H$\beta$ spaxels.