Extreme-value modelling of the brightest galaxies at z ≳ 9

ABSTRACT Data from the JWST have revealed an intriguing population of bright galaxies at high redshifts. In this work, we use extreme-value statistics to calculate the distribution in ultraviolet (UV) magnitude of the brightest galaxies in the redshift range 9 z 16. We combine the generalized extreme-value approach with modelling of the galaxy luminosity function. We obtain predictions of the brightest galaxies for a suite of luminosity functions, including the Schechter and double power-law functions, as well as a model parametrized by the stellar formation efficiency f_*. We find that the JWST data are broadly consistent with f_* of 5\!\!-\!\!10{\ per\, cent}, and that the brightest galaxy at z 16 will have M ₔₕ -23. 5^0. 8₀. ₄. If f_* is dependent on halo mass, we predict M ₔₕ -22. 5^0. 5₁. ₅ for such an object. We show that extreme-value statistics not only predict the magnitude of the brightest galaxies at high redshifts, but may also be able to distinguish between models of star formation in high-redshift galaxies.