We report {\em JWST}/NIRCam measurements of quasar host galaxy emissions and
supermassive black hole (SMBH) masses for six quasars at 5.9<z<7.1 in the
\textit{Emission-line galaxies and Intergalactic Gas in the Epoch of
Reionization} (EIGER) project. We obtain deep NIRCam imaging in the F115W,
F200W, and F356W bands, as well as F356W grism spectroscopy of the quasars. We
use bright unsaturated stars to construct models of the point spread function
(PSF) and estimate the errors of these PSFs. We then measure or constrain the
fluxes and morphology of the quasar host galaxies by fitting the quasar images
as a point source plus an exponential disk. We successfully detect the host
galaxy of three quasars, which have host-to-quasar flux ratios of
βΌ1%β5%. Spectral Energy Distribution (SED) fitting suggests that these
quasar host galaxies have stellar masses of Mβββ³1010Mββ. For
quasars with host galaxy non-detections, we estimate the upper limits of their
stellar masses. We use the grism spectra to measure the {\hb} line profile and
the continuum luminosity, then estimate the SMBH masses for the quasars. Our
results indicate that the positive relation between SMBH masses and host galaxy
stellar masses already exists at redshift zβ³6. The quasars in our
sample show a high black hole to stellar mass ratio of
MBHβ/MβββΌ0.15, which is about βΌ1β2 dex higher than the local
relations. This result suggests that luminous quasars at zβ³6 form a
biased sample with overmassive black holes, which might have experienced early
SMBH growth compared to their host galaxies' star formation.Comment: 21 pages, 12 figures, submitted to AAS journals. Comments welcome