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

Abstract

Luminous quasars at the redshift frontier z > 7 serve as stringent probes of super-massive black hole (SMBH) 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 (BLR) to the interstellar and circumgalactic medium (ISM and CGM). The James Webb Space Telescope (JWST) now provides the necessary spatially resolved spectroscopy to do so. However, 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 integral field unit (IFU) observations of J0313−1806 at z = 7.64, the most distant luminous quasar known. From the rest-frame optical spectrum of the unresolved quasar, we derived a black hole mass of MBH = (1.63 ± 0.10)×109 M⊙ based on Hβλ4861 (Hβ) and an Eddington rate of λ = L/LEdd = 0.80 ± 0.05, consistent with previous Mg II λ2800-based estimates. J0313–1806 exhibits no detectable [O III] λλ4959, 5007 emission on nuclear scales (3σ upper limit equivalent width of [O III] λ5007 < 1.42 Å). Most remarkably, we did detect an ionized gas shell extending out to ∼1.8 kpc traced by Hβ emission that also lacks any significant [O III] λλ4959, 5007, with a 3σ upper limit on the [O III] λ5007 to Hβ flux ratio of log10(F([O III])/F(Hβ)) = −1.15. Through photoionization modeling, we demonstrate that the extended emission is consistent with a thin, clumpy outflowing shell where [O III] 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 across cosmic time.