We report the discovery of 15 exceptionally luminous 10β²zβ²14
candidate galaxies discovered in the first 0.28 deg2 of JWST/NIRCam imaging
from the COSMOS-Web Survey. These sources span rest-frame UV magnitudes of
β20.5>MUVβ>β22, and thus constitute the most intrinsically luminous
zβ³10 candidates identified by JWST to-date. Selected via NIRCam imaging
with Hubble ACS/F814W, deep ground-based observations corroborate their
detection and help significantly constrain their photometric redshifts. We
analyze their spectral energy distributions using multiple open-source codes
and evaluate the probability of low-redshift solutions; we conclude that 12/15
(80%) are likely genuine zβ³10 sources and 3/15 (20%) likely
low-redshift contaminants. Three of our zβΌ12 candidates push the limits of
early stellar mass assembly: they have estimated stellar masses
βΌ5Γ109Mββ, implying an effective stellar baryon fraction of
Ο΅βββΌ0.2β0.5, where Ο΅βββ‘Mββ/(fbβMhaloβ). The assembly of such stellar reservoirs is made
possible due to rapid, burst-driven star formation on timescales <100\,Myr
where the star-formation rate may far outpace the growth of the underlying dark
matter halos. This is supported by the similar volume densities inferred for
MβββΌ1010Mββ galaxies relative to MβββΌ109Mββ
-- both about 10β6 Mpcβ3 -- implying they live in halos of comparable
mass. At such high redshifts, the duty cycle for starbursts would be of order
unity, which could cause the observed change in the shape of the UVLF from a
double powerlaw to Schechter at zβ8. Spectroscopic redshift
confirmation and ensuing constraints of their masses will be critical to
understanding how, and if, such early massive galaxies push the limits of
galaxy formation in ΞCDM.Comment: 30 pages, 9 figures; ApJ submitte