Observing EAGLE galaxies with JWST: predictions for Milky Way
  progenitors and their building blocks
  We present predictions, derived from the EAGLE $\Lambda$CDM cosmological
hydrodynamical simulations, for the abundance and of galaxies expected to be
detected at high redshift by the {\it James Webb Space Telescope} (\JWST). We
consider the galaxy as a whole and focus on the sub-population of progenitors
of Milky Way (MW) analogues, defined to be galaxies with accretion histories
similar to the MW's, that is, galaxies that underwent a merger the
Gaia-Enceladus-Sausage (GES) event and that contain an analogue of the Large
Magellanic Cloud (LMC) satellite today. We the luminosity function of all EAGLE
galaxies in \JWST/NIRCam passbands, in the redshift range $z=2-8$, taking into
account dust obscuration and different exposure times. For an exposure time of
$T=10^5$s, average MW progenitors are observable as far back as $z\sim6$ in
most bands, and this changes to $z\sim5$ and $z\sim4$ for the GES and LMC
progenitors, respectively. The progenitors of GES and LMC analogues are, on
average, $\sim 2$ and $\sim 1$ mag fainter than the MW progenitors at most
redshifts. They lie, on average, within $\sim 60$ and $30$ arcsec,
respectively, of their future MW host at all times, and thus will appear within
the field-of-view of \JWST/NIRCam. We conclude that galaxies resembling the
main progenitor of the MW and its major accreted components should be
observable with \JWST\ beyond redshift $2$, providing a new and unique window
in studying the formation history of our own galaxy.
