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 study 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.

References

However, beyond $z=13.5$ there is a noticeable dearth in the total $p(z)$ and therefore we are unable to precisely measure the UV LF at this redshift.

— JWST PRIMER: A new multi-field determination of the evolving galaxy UV luminosity function at redshifts $\mathbf{z \simeq 9-15}$  (2403.03171 - Donnan et al., 2024) in Section 4, UV Luminosity function (paragraph preceding Fig. 9)

Given the small size of the current sample, it is too early to draw any firm conclusion from this result: wider surveys are needed to establish whether this trend is real or an effect of the limited sample.

— Too many or too bright? Status and perspectives in the study of the UV Luminosity Function at z>10  (2610.12121 - Fontana et al., 8 Oct 2026) in Appendix, discussion following Figure \ref{fig:evolutionari_fit}