Prospects for distinguishing galaxy evolution models with surveys at
  redshifts $z \gtrsim 4$
  Many semi-empirical galaxy formation models have recently emerged to
interpret high-$z$ galaxy luminosity functions and make predictions for future
galaxy surveys. A common approach assumes a "universal" star formation
efficiency, $f_{\ast}$, independent of cosmic time but strongly dependent on
the masses of dark matter halos. Though this class of models has been very
successful in matching observations over much of cosmic history, simple stellar
feedback models do predict redshift evolution in $f_{\ast}$, and are commonly
used in semi-analytic models. In this work, we calibrate a set of universal
$f_{\ast}$ and feedback-regulated models to the same set of rest-ultraviolet $z
\gtrsim 4$ observations, and find that a rapid, $\sim (1+z)^{-3/2}$ decline in
both the efficiency of dust production and duty cycle of star formation are
needed to reconcile feedback-regulated models with current observations. By
construction, these models remain nearly identical to universal $f_{\ast}$
models in rest-ultraviolet luminosity functions and colours. As a result, the
only way to distinguish these competing scenarios is either via (i) improved
constraints on the clustering of galaxies -- universal and feedback-regulated
models differ in predictions for the galaxy bias by $0.1 \lesssim \Delta
\langle b \rangle \lesssim 0.3$ over $4 \lesssim z \lesssim 10$ -- or (ii)
independent constraints on the dust contents and/or duty cycle of star
formation. This suggests that improved constraints on the `dustiness' and
`burstiness' of high-$z$ galaxies will not merely add clarity to a given model
of star formation in high-$z$ galaxies, but rather fundamentally determine our
ability to identify the correct model in the first place.
