2025ApJ...992...63W

The high-redshift UV luminosity function provides important insights into the evolution of early galaxies. JWST has revealed an unexpectedly large population of bright (M_UV ≲ -20) galaxies at z ≳ 10, implying fundamental changes in the star-forming properties of galaxies at increasingly early times. However, constraining the fainter population (M_UV ≳ -18) has been more challenging. In this work, we present the z ≳ 9 UV luminosity function from the JWST Advanced Deep Extragalactic Survey. We calculate the UV luminosity function from several hundred z ≳ 9 galaxy candidates that reach UV luminosities of M_UV ∼ -17 in redshift bins of z ∼ 8.5-12 (309 candidates) and z ∼ 12-16 (63 candidates). We search for candidates at z ∼ 16-22.5 and find none. We also estimate the z ∼ 14-16 luminosity function from the z ≥ 14 subset of the z ∼ 12-16 sample. Consistent with other measurements, we find an excess of bright galaxies that is in tension with many theoretical models, especially at z ≳ 12. However, we also find high number densities at -18 ≲ M_UV ≲ -17, suggesting that there is a larger population of faint galaxies than expected, as well as bright ones. From our parametric fits for the luminosity function, we find steep faint-end slopes of -2.5 ≲ α ≲ -2.3, suggesting a large population of faint (M_UV ≳ -17) galaxies. Combined, the high normalization and steep faint-end slope of the luminosity function could imply that the reionization process is appreciably underway as early as z = 10.