Direct pathway to the Early Supermassive Black Holes: A Red Super-Eddington Quasar in a Massive Starburst Host at $z=7.2$

Qinyue Fei, Seiji Fujimoto, Gabriel Brammer, Ruancun Li, Luis C. Ho, Volker Bromm, Javier Álvarez-Márquez, Yoshihisa Asada, Guillermo Barro, Luis Colina, Pratika Dayal, Steven L. Finkelstein, Johan P. U. Fynbo, Michele Ginolfi, Kohei Inayoshi, Vasily Kokorev, Gene C. K. Leung, Jorryt Matthee, Romain A. Meyer, Rohan P. Naidu, Masafusa Onoue, Pablo G. Pérez-González, Charles L. Steinhardt, Francesco Valentino, Fabian Walter, Mengyuan Xiao, Haowen Zhang

First listed 2026-02-12 | Last updated 2026-02-16

Abstract

We present a panchromatic optical-mm characterization of GNz7q, a recently identified X-ray weak, rapidly growing red quasar embedded within a dusty starburst galaxy at $z=7.1899$, using the full suite of JWST/NIRCam, NIRSpec, MIRI, and archival NOEMA observations. Our deep NIRSpec/G395M spectroscopy reveals unambiguous broad Balmer emission (FWHM $=2221\pm20$kms$^{-1}$), confirming a super-Eddington accreting black hole ($λ_{\rm Edd}=2.7\pm0.4$) with a mass of $\log(M_{\rm BH}/M_{\odot})=7.55\pm0.34$, using accretion-rate corrected BH mass estimators. After subtracting the point source, we robustly detect stellar emission from the host galaxy across multiple NIRCam and MIRI filters. Out joint morphological-spectral analysis yields a stellar mass of $\log (M_*/M_\odot)=10.5\pm0.4$ and an intense star formation rate of ${\rm SFR}=330\pm97\,M_\odot\,\rm yr^{-1}$, confirming the host as a massive, dusty starburst galaxy. We find that GNz7q lies on the local $M_{\rm BH}$-$M_*$ relation ($M_{\rm BH}/M_*\simeq 0.001$) and is well positioned to evolve into the locus of massive SDSS quasars with $\log (M_{\rm BH}/M_\odot)\approx 9$ and $M_*\approx 10^{11}\,M_\odot$ at $z\sim 6$, owing to its remarkably rapid growth in both the black hole and its host galaxy. This stands in stark contrast to many recently reported JWST AGN populations at similar redshifts, including the little red dots (LRDs), whose weak or undetected star formation makes it difficult for them to grow into the massive galaxies hosting SDSS-like quasars. These results suggest that GNz7q marks as a rare, pivotal phase of early BH-galaxy co-eolution, plausibly providing a crucial direct pathway to the supermassive black hole systems within the first billion years of the Universe.

Short digest

GNz7q at z=7.1899 is panchromatically dissected with JWST (NIRCam/NIRSpec/MIRI) plus NOEMA, revealing an X-ray‑weak, rapidly growing red quasar embedded in a dusty starburst. Deep NIRSpec/G395M shows clear broad Balmer lines (FWHM 2221±20 km s^-1), implying a super‑Eddington SMBH (λEdd=2.7±0.4) with log(MBH/M⊙)=7.55±0.34 from accretion‑rate–corrected virial estimates. PSF‑subtracted imaging recovers a massive, actively star‑forming host with log(M*/M⊙)=10.5±0.4 and SFR=330±97 M⊙ yr^-1, placing GNz7q on the local MBH–M* relation (MBH/M*≈0.001). Unlike many little red dots with weak/undetected SF, GNz7q looks like a rare transitional phase en route to the massive z~6 quasar locus, outlining a direct pathway to early SMBHs.

Key figures to inspect

• Fig. 1 (NIRSpec spectrum and model): Verify the continuum+Fe II decomposition and the broad Balmer fit that drives the λEdd and MBH inference; check residuals for missed absorption or template mismatches.
• Fig. 2 (Zoom on Balmer lines): Inspect the Hβ/Hγ profiles and the two-component BLR (including the redshifted rBLR) that underpins the super‑Eddington interpretation and the precise FWHM measurement.
• Fig. 3 (MIRI MRS Paα map and spectrum): Confirm a compact, nuclear recombination line and evaluate residuals; use the spatial concentration and line strength to gauge embeddedness/extinction consistent with an X‑ray‑weak red quasar.
• Fig. 4 (Multi-band AGN–host decomposition): Assess PSF subtraction across filters, host morphology/extent, and residual structure that set the stellar mass and imply a dusty starburst (driving the quoted SFR).