  Early photometric results from JWST have revealed a number of galaxy
candidates above redshift 10. The initial estimates of inferred stellar masses
and the associated cosmic star formation rates are above most theoretical model
predictions up to a factor of 20 in the most extreme cases, while this has been
moderated after the recalibration of NIRCam and subsequent spectroscopic
detections. Using these recent JWST observations, we use galaxy scaling
relations from cosmological simulations to model the star formation history to
very high redshifts, back to a starting halo mass of 10^7 solar masses, to
infer the intrinsic properties of the JWST galaxies. Here we explore the
contribution of supermassive black holes, stellar binaries, and an excess of
massive stars to the overall luminosity of high-redshift galaxies. Despite the
addition of alternative components to the spectral energy distribution, we find
stellar masses equal to or slightly higher than previous stellar mass
estimates. Most galaxy spectra are dominated by the stellar component, and the
exact choice for the stellar population model does not appear to make a major
difference. We find that four of the 12 high-redshift galaxy candidates are
best fit with a non-negligible active galactic nuclei component, but the
evidence from the continuum alone is insufficient to confirm their existence.
Upcoming spectroscopic observations of z > 10 galaxies will confirm the
presence and nature of high-energy sources in the early universe and will
constrain their exact redshifts.

Astrophysics of Galaxies