We present results from the Cosmic Evolution Early Release Survey (CEERS) on
the stellar-population parameters for 28 galaxies with redshifts 4<z<9 using
imaging data from the James Webb Space Telescope (JWST) Mid-Infrared Instrument
(MIRI) combined with data from the Hubble Space Telescope and the Spitzer Space
Telescope. The JWST/MIRI 5.6 and 7.7 μm data extend the coverage of the
rest-frame spectral-energy distribution (SED) to nearly 1 micron for galaxies
in this redshift range. By modeling the galaxies' SEDs the MIRI data show that
the galaxies have, on average, rest-frame UV (1600 \r{A}) −I-band colors
0.4 mag bluer than derived when using photometry that lacks MIRI. Therefore,
the galaxies have lower (stellar)-mass-to-light ratios. The MIRI data reduce
the stellar masses by ⟨ΔlogM∗⟩=0.25 dex at 4<z<6 (a
factor of 1.8) and 0.37 dex at 6<z<9 (a factor of 2.3). This also reduces the
star-formation rates (SFRs) by ⟨ΔlogSFR⟩=0.14
dex at 4<z<6 and 0.27 dex at 6<z<9. The MIRI data also improve constraints
on the allowable stellar mass formed in early star-formation. We model this
using a star-formation history that includes both a "burst' at zf=100 and a
slowly varying ("delayed-τ") model. The MIRI data reduce the allowable
stellar mass by 0.6 dex at 4<z<6 and by ≈1 dex at 6<z<9. Applying
these results globally, this reduces the cosmic stellar-mass density by an
order of magnitude in the early universe (z≈9). Therefore, observations
of rest-frame ≳1 μm are paramount for constraining the stellar-mass
build-up in galaxies at very high-redshifts.Comment: Updated with accepted ApJ version. Part of the CEERS Focus Issue. 27
pages, many figures (4 Figure Sets, available upon reasonable request