Affiliation: University of Edinburgh

Contribution: Oral

Title: JWST PRIMER: A new multi-field determination of the evolving galaxy UV luminosity function at z=9-15

Abstract: I will present a new determination of the evolving galaxy UV luminosity function (LF) over the redshift range 8.5<z<15.5 using a combination of several major Cycle-1 JWST imaging programmes – PRIMER, JADES and NGDEEP. This multi-field approach yields a total of ~37 0sq. arcmin of JWST/NIRCam imaging, reaching (5-sigma) depths of ~30 AB mag in the deepest regions. We select a sample of 2548 galaxies with a significant probability of lying at high redshift (p(z>8.5)>0.05) to undertake a statistical calculation of the evolving UV LF. Our new measurements span ~4 magnitudes in UV luminosity at z=9-12.5, placing new constraints on both the shape and evolution of the LF at early times. We fit our observational data-points with a double-power law (DPL) function and explore the evolution of the DPL parameters. Our UV LF measurements yield a new estimate of the early evolution of cosmic star-formation rate density (SFRD) which confirms the gradual, log-linear decline deduced from early JWST studies, at least out to z~12. Finally, I will show that the observed early evolution of the galaxy UV LF (and SFRD) can be reproduced in a LCDM Universe, with no change in dust properties or star-formation efficiency required out to z~12. Instead, we find that a progressive trend towards younger stellar population ages can reproduce the observations, and we show that the typical ages required at z = 8, 9, 10, and 11 all converge on a time ~380-330 Myr after the Big Bang, indicative of a rapid emergence of early galaxies at z=12-13. This is consistent with the first indications of a steeper drop-off in the galaxy population we find beyond z=13, possibly reflecting the rapid evolution of the halo mass function at earlier times.

This contribution can be found here (pdf).