Dark-ages reionization and galaxy-formation simulation - VI. The origins
  and fate of the highest known redshift galaxy
  Using Hubble data, including new grism spectra, Oesch et al. recently
identified GN-z11, an $M_\textrm{UV}$=-21.1 galaxy at $z$=11.1 (just 400Myr
after the big bang). With an estimated stellar mass of $\sim$10$^9$M$_{\odot}$,
this galaxy is surprisingly bright and massive, raising questions as to how
such an extreme object could form so early in the Universe. Using \Meraxes{}, a
semi-analytic galaxy-formation model developed as part of the Dark-ages
Reionization And Galaxy-formation Observables from Numerical Simulations
(DRAGONS) programme, we investigate the potential formation mechanisms and
eventual fate of GN-z11. The volume of our simulation is comparable to that of
the discovery observations and possesses two analogue galaxies of similar
luminosity to this remarkably bright system. Existing in the two most massive
subhaloes at $z$=11.1 ($M_\textrm{vir}$=1.4$\times 10^{11}$M$_{\odot}$ and
6.7$\times 10^{10}$M$_{\odot}$), our model analogues show excellent agreement
with all available observationally derived properties of GN-z11. Although they
are relatively rare outliers from the full galaxy population at high-$z$, they
are no longer the most massive or brightest systems by $z$=5. Furthermore, we
find that both objects possess relatively smooth, but extremely rapid mass
growth histories with consistently high star formation rates and UV
luminosities at $z{>}11$, indicating that their brightness is not a transient,
merger-driven feature. Our model results suggest that future wide-field surveys
with the \textit{James Webb Space Telescope} may be able to detect the
progenitors of GN-z11 analogues out to $z{\sim}$13--14, pushing the frontiers
of galaxy-formation observations to the early phases of cosmic reionization and
providing a valuable glimpse of the first galaxies to reionize the Universe on
large scales.
