No evidence (yet) for increased star-formation efficiency at early times

Understand

Early JWST observations have revealed substantial numbers of galaxies out to redshifts as high as $z \simeq 14$, reflecting a slow evolution of the galaxy UV luminosity function (LF) not anticipated by many models of galaxy evolution.

• The discovery of fairly massive galaxies at early times has again been viewed as a challenge to our understanding of early galaxy growth or even ${\rm \Lambda}$CDM cosmology.
• Here we develop and test a simple theoretical model which shows that these observations are unsurprising, but instead are arguably as expected if one assumes a non-evolving halo-mass dependent galaxy-formation efficiency consistent with that observed today.
• Crucially, this model matches the observed galaxy UV LF at $z \simeq 6-13$ and the galaxy stellar mass function (GSMF) at $z \simeq 6-8$.