Data from "Detection of the Low-Mass Host Galaxy of a z~6.25 Quasar with JWST"

We characterize the stellar mass of J2239+0207, a z ∼ 6.25 sub-Eddington quasar (M1450 = −24.6),
using dedicated JWST/NIRCam medium-band observations of a nearby PSF star to remove the central
point source and reveal the underlying galaxy emission. We detect the host galaxy in two bands
longward of the Balmer break, and via calibration to existing Spitzer/IRAC data obtain a stellar
mass of ∼ 1010 M⊙, more than an order of magnitude less than this quasar’s existing measured [C II]
dynamical mass. We additionally calculate the mass of J2239+0207’s central supermassive black hole
using JWST/NIRSpec IFU observations, and determine that the black hole is ∼ 15 times more massive
than predicted by the local MBH-M∗ relation, similar to many high-redshift quasars with dynamical
masses determined via millimeter-wave line widths. We carefully consider potential selection effects
at play, and find that even when the z ∼ 6 quasars are compared to a local sample with similarly
determined dynamical masses, the high-redshift quasars appear to possess overmassive black holes. We
conclude z ∼ 6 quasars are likely to have a larger spread about the MBH-M∗ relation than observed
in the local Universe.