Beyond UV: Rest-frame B-band and Apparent Luminosity Functions of z=5-9 Galaxies

TL;DR

This study uses JWST data to measure galaxy luminosity functions from redshift 4.5 to 9.7, revealing new insights into galaxy evolution, the limitations of current models, and the importance of rest-frame optical observations in understanding early galaxy formation.

Contribution

First constraints on the rest-frame B-band luminosity function at z~7-8 and extended measurements at z~5, highlighting evolution differences and discrepancies with simulations.

Findings

B-band LFs evolve more strongly than UV LFs with redshift.

Observed LFs decline more gradually than simulations predict at z>5.

Hints of a bright-end excess in apparent LFs, possibly due to dusty or obscured galaxies.

Abstract

We present new measurements of galaxy luminosity functions (LFs) from JWST/NIRCam imaging over the redshift range z=4.5-9.7, using photometric catalogs from JADES and public extragalactic fields. Our analysis includes rest-frame UV and B-band LFs, as well as apparent LFs in F090W, F115W, F200W, F356W, and F444W. We present the first constraints on the rest-frame B-band LF at z~7-8 and extend existing measurements at z~5 to M(B) = -18 mag. The B-band LFs evolve more strongly with redshift than UV LFs, though both decline more gradually than predicted by simulations at z>5. No single existing simulation reproduces all observed trends, with discrepancies likely driven by assumptions about binary evolution and stellar population synthesis models. The apparent LFs in F356W and F444W show hints of a bright-end excess at all redshifts, extending to fainter magnitudes at higher redshift. While extreme emission line galaxies may partially account for it, the excess may also indicate a population of moderately red, optically bright sources - potentially dusty star-forming galaxies or obscured AGNs. Finally, we find that rest-frame B-band luminosity correlates more tightly with stellar mass than UV, making it a powerful tracer of mass assembly and reinforcing the diagnostic value of rest-frame optical LFs in uncovering the physical processes that drive early galaxy formation.