Why are UV-bright galaxies at redshift above 10 so abundant?
In plain words
JWST sees many more bright galaxies in the first 500 million years than models built before its launch predicted. Either early galaxies made stars much more efficiently, or something else is different.
Precise statement
The number density of galaxies with $M_{\mathrm{UV}} < -20$ at $z \sim 10\ \text{to}\ 15$ exceeds pre-JWST models by factors of 10 to 100 (the spectroscopically confirmed MoM-z14 at $z = 14.44$ implies a factor $\sim 100$ at $z \sim 14$). Identify the mechanism: high star-formation efficiency (feedback-free starbursts), bursty star formation, a top-heavy initial mass function, negligible dust, active-galactic-nucleus light, or enhanced small-scale primordial power. An answer reproduces the UV luminosity function at $z = 10\ \text{to}\ 15$ together with clustering and spectral constraints.
What would settle it
Clustering measurements of $z > 10$ galaxies giving their halo masses, combined with spectroscopic constraints on stellar populations and burstiness.
Status in the literature
Unverified note
2025 confirmation of MoM-z14 at $z = 14.44$ extended the excess to 280 million years after the Big Bang.
See also
- Related Do any early JWST galaxies exceed the LCDM baryon budget?
- Related Do early galaxies overproduce ionizing photons for reionization?
- Related Were the first black hole seeds light or heavy?
- Related Why does gas form stars at only one percent per free-fall time?
- Related Was the IMF top-heavy in the first galaxies?