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 approximate to -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 approximate to 0.1 Z(circle dot) even at z = 7-8. Most of the simulated galaxies at z approximate to 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 per cent) 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. Pop III 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 per cent 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.