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JWST observations have revealed a population of galaxies bright enough thatpotentially challenge standard galaxy formation models in the $\Lambda$CDMcosmology. Using a minimal empirical framework, we investigate the influence ofvariability on the rest-frame ultra-violet (UV) luminosity function (UVLF) ofgalaxies at $z\geq 9$. Our study differentiates between the $\textit{median UVradiation yield}$ and the $\textit{variability of UV luminosities}$ of galaxiesat a fixed dark matter halo mass. We primarily focus on the latter effect,which depends on halo assembly and galaxy formation processes and cansignificantly increase the abundance of UV-bright galaxies due to the upscatterof galaxies in lower-mass haloes. We find that a relatively low level ofvariability, $\sigma_{\rm UV} \approx 0.75$ mag, matches the observationalconstraints at $z\approx 9$. However, increasingly larger $\sigma_{\rm UV}$ isnecessary when moving to higher redshifts, reaching $\sigma_{\rm UV} \approx2.0\,(2.5)\,{\rm mag}$ at $z\approx 12$ ($16$). This implied variability isconsistent with expectations of physical processes in high-redshift galaxiessuch as bursty star formation and cycles of dust clearance. Photometricconstraints from JWST at $z\gtrsim 9$ therefore can be reconciled with astandard $\Lambda$CDM-based galaxy formation model calibrated at lowerredshifts without the need for adjustments to the median UV radiation yield.

The impact of UV variability on the abundance of bright galaxies at $z \geq 9$