  During the first 500 million years of cosmic history, the first stars and
galaxies formed, seeding the Universe with heavy elements and eventually
reionizing the intergalactic medium. Observations with JWST have uncovered a
surprisingly high abundance of candidates for early star-forming galaxies, with
distances (redshifts, $z$), estimated from multi-band photometry, as large as
$z\approx 16$, far beyond pre-JWST limits. While generally robust, such
photometric redshifts can suffer from degeneracies and occasionally
catastrophic errors. Spectroscopic measurement is required to validate these
sources and to reliably quantify physical properties that can constrain galaxy
formation models and cosmology. Here we present JWST spectroscopy that confirms
redshifts for two very luminous galaxies with $z > 11$, but also demonstrates
that another candidate with suggested $z\approx 16$ instead has $z = 4.9$, with
an unusual combination of nebular line emission and dust reddening that mimics
the colors expected for much more distant objects. These results reinforce
evidence for the early, rapid formation of remarkably luminous galaxies, while
also highlighting the necessity of spectroscopic verification. The large
abundance of bright, early galaxies may indicate shortcomings in current galaxy
formation models, or deviation from physical properties (such as the stellar
initial mass function) that are generally believed to hold at later times.
