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[Abridged] Understanding how the intergalactic medium (IGM) was reionized atz > 6 is one of the big challenges of current high redshift astronomy. Itrequires modelling the collapse of the first astrophysical objects (Pop IIIstars, first galaxies) and their interaction with the IGM, while at the sametime pushing current observational facilities to their limits. Theobservational and theoretical progress of the last few years have led to theemergence of a coherent picture in which the budget of hydrogen-ionizingphotons is dominated by low-mass star-forming galaxies, with littlecontribution from Pop III stars and quasars. The reionization history of theUniverse therefore critically depends on the number density of low-massgalaxies at high redshift. In this work, we explore how changes in thestatistical properties of initial density fluctuations affect the formation ofearly galaxies. Following Habouzit et al. (2014), we run 5 N-body simulationswith Gaussian and (scale-dependent) non-Gaussian initial conditions, allconsistent with Planck constraints. By appealing to a galaxy formation modeland to a population synthesis code, we compute the far-UV galaxy luminosityfunction down to M_UV = -14 at redshift 7 < z < 15. We find that models withstrong primordial non-Gaussianities on < Mpc scales show a far-UV luminosityfunction significantly enhanced in low-mass galaxies. We adopt a reionizationmodel calibrated from state-of-the-art hydrodynamical simulations and show thatsuch non-Gaussianities leave a clear imprint on the Universe reionizationhistory and electron Thomson scattering optical depth tau_E. Although currentuncertainties in the physics of reionization and on the determination of tau_Estill dominate the signatures of non-Gaussianities, our results suggest thattau_E could ultimately be used to constrain the statistical properties ofinitial density fluctuations.

Effect of primordial non-Gaussianities on the far-UV luminosity function of high-redshift galaxies: implications for cosmic reionization