Extreme-value modelling of the brightest galaxies at $z\gtrsim 9$

Abstract

Data from the James Webb Space Telescope have revealed an intriguing population of bright galaxies at high redshifts. In this work, we use extreme-value statistics to calculate the distribution (in UV magnitude) of the brightest galaxies in the redshift range $9\lesssim z\lesssim 16$. We combine the Generalised Extreme Value (GEV) 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 parametrised by the stellar formation efficiency $f_{\ast }$. We find that the JWST data is broadly consistent with $f_{\ast }$ of $5\%-10\%$, and that the brightest galaxy at $z\sim 16$ will have $M_{\mathrm{UV}}\approx -23.5_{0.4}^{0.8}$. If $f_{\ast }$ is dependent on halo mass, we predict $M_{\mathrm{UV}}\approx -22.5_{1.5}^{0.5}$ for such an object. We show that extreme-value statistics not only predicts 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.

10 pages, 8 figures, MNRAS accepted