Simulating high-redshift galaxies
  Recent observations have gathered a considerable sample of high redshift
galaxy candidates and determined the evolution of their luminosity function
(LF). To interpret these findings, we use cosmological SPH simulations
including, in addition to standard physical processes, a detailed treatment of
the Pop III-Pop II transition in early objects. The simulated high-z galaxies
match remarkably well the amplitude and slope of the observed LF in the
redshift range 5<z<10. The LF shifts towards fainter luminosities with
increasing redshift, while its faint-end slope keeps an almost constant value,
\alpha ~-2. The stellar populations of high-z galaxies have ages of 100-300
(40-130) Myr at z=5 (z=7-8), implying an early (z>9.4) start of their star
formation activity; the specific star formation rate is almost independent of
galactic stellar mass. These objects are enriched rapidly with metals and
galaxies identified by HST/WFC3 (M_UV < -18) show metallicities ~0.1 Zsun even
at z=7-8. Most of the simulated galaxies at z~7 (noticeably the smallest ones)
are virtually dust-free, and none of them has an extinction larger than E(B-V)
= 0.01. The bulk (50%) of the ionizing photons is produced by objects
populating the faint-end of the LF (M_UV < -16), which JWST will resolve up to
z=7.3. PopIII stars continue to form essentially at all redshifts; however, at
z=6 (z=10) the contribution of Pop III stars to the total galactic luminosity
is always less than 5% for M_UV < -17 (M_UV < -16). The typical high-z galaxies
closely resemble the GRB host galaxy population observed at lower redshifts,
strongly encouraging the use of GRBs to detect the first galaxies.
