Detection of stellar light from quasar host galaxies at redshifts above 6.

The detection of starlight from the host galaxies of quasars during the reionization epoch (z > 6) has been elusive, even with deep Hubble Space Telescope observations ^1,2 . The current highest redshift quasar host detected ³ , at z = 4.5, required the magnifying effect of a foreground lensing galaxy. Low-luminosity quasars ^4-6 from the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) ⁷ mitigate the challenge of detecting their underlying, previously undetected host galaxies. Here we report rest-frame optical images and spectroscopy of two HSC-SSP quasars at z > 6 with the JWST. Using near-infrared camera imaging at 3.6 and 1.5 μm and subtracting the light from the unresolved quasars, we find that the host galaxies are massive (stellar masses of 13 × and 3.4 × 10 ¹⁰  M _☉ , respectively), compact and disc-like. Near-infrared spectroscopy at medium resolution shows stellar absorption lines in the more massive quasar, confirming the detection of the host. Velocity-broadened gas in the vicinity of these quasars enables measurements of their black hole masses (1.4 × 10 ⁹ and 2.0 × 10 ⁸  M _☉ , respectively). Their location in the black hole mass-stellar mass plane is consistent with the distribution at low redshift, suggesting that the relation between black holes and their host galaxies was already in place less than a billion years after the Big Bang.
(© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)