The z > 9 galaxy UV luminosity function from the JWST Advanced Deep Extragalactic Survey: insights into early galaxy evolution and reionization

The high-redshift UV luminosity function provides important insights into the evolution of early galaxies. JWST has revealed an unexpectedly large population of bright ($M_{\mathrm{UV}} \lesssim −20$ ) galaxies at $z \gtrsim 10$ , implying fundamental changes in the star forming properties of galaxies at increasingly early times. However, constraining the fainter population ($M_{\mathrm{UV}} \gtrsim −18$ ) has been more challenging. In this work, we present the $z \gtrsim 9$ UV luminosity function from the JWST Advanced Deep Extragalactic Survey. We calculate the UV luminosity function from several hundred $z \gtrsim 9$ galaxy candidates that reach UV luminosities of $M_{\mathrm{UV}} \sim −17$ in redshift bins of $z \sim 9−12$ (309 candidates) and $z \sim 12−16$ (63 candidates). We search for candidates at $z \sim 16−22.5$ and find none. We also estimate the $z \sim 14−16$ luminosity function from the $z \gtrsim 14$ subset of the $z \sim 12−16$ sample. Consistent with other measurements, we find an excess of bright galaxies that is in tension with many theoretical models, especially at $z \gtrsim 12$ . However, we also find high number densities at $−18 \lesssim M_{\mathrm{UV}} \lesssim −17$ , 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 $−2.5 \lesssim \alpha \lesssim −2.3$ , suggesting a large population of faint ($M_{\mathrm{UV}} \gtrsim −17$ ) 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 $z = 10$ .

eprint arXiv:2501.00984