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The Ultraviolet Luminosity Function (UVLF) is a key observable forunderstanding galaxy formation from cosmic dawn. There has been considerabledebate on whether Schechter-like LFs (characterized by an exponential drop-offat the bright end) that well describe the LF in our local Universe are also asufficient description of the LF at high redshifts ($z>6$). We model the UVLFover cosmic history with a semi-empirical framework and include a log-normalscatter, $\Sigma$, in galaxy luminosities with a conditional luminosityfunction approach. We show that stochasticity induces a flattening or afeedback scale in the median galaxy luminosity versus halo mass relation,$L_{c}(M_{h})$ to account for the increase of bright objects placed in lowermass halos. We observe a natural broadening in the bright-end exponentialsegment of the UVLF for $z>6$ if processes that regulate star-formation acts onthe same mass scale as at $z\sim5$, where the degree of broadening is enhancedfor larger $\Sigma$. Alternatively, if the bright-end feedback is triggered ata near-constant luminosity threshold, the feedback threshold occurs atprogressively lower halo masses with increasing redshift, due to galaxies beingmore luminous on average at a fixed halo mass from rapid halo assembly. Suchfeedback results in a LF shape with a bright-end closer to that of a Schechterfunction. We include predictions for the $z>8$ UVLFs from future all-skysurveys such as WFIRST which has the potential to both quantify the scatter andtype of feedback, and provide insight behind the mechanisms that drive starformation in the early Universe.

The Brightest Galaxies at Cosmic Dawn from Scatter in the Galaxy Luminosity versus Halo Mass Relation