Precisely measure the galaxy UV luminosity function at z ≥ 13.5

Determine the rest-frame ultraviolet galaxy luminosity function at redshifts z ≥ 13.5 with sufficient precision to overcome the current paucity of high-redshift candidates that prevents a precise measurement.

Background

The paper combines multiple JWST NIRCam surveys (PRIMER, JADES, NGDEEP) to measure the galaxy UV luminosity function robustly across z = 9–12.5, spanning about four magnitudes in UV luminosity without relying on lensing fields.

Despite these advances, the authors report that beyond z = 13.5 the aggregate redshift probability p(z) is too low to enable a precise measurement of the UV luminosity function. They present only a tentative single bin at z ≃ 14.5 based on an effective total p(z) equivalent to approximately 1.3 galaxies, emphasizing the need for improved constraints.

A precise determination of the UV luminosity function at z ≥ 13.5 is crucial for confirming whether the smooth decline in cosmic star-formation rate density seen at z = 9–12.5 transitions to a steeper drop at earlier times, thereby informing models of early galaxy formation and the rapid evolution of the halo mass function.