Monsters in the dark: predictions for luminous galaxies in the early Universe from the BLUETIDES simulation

Abstract

Using deep Hubble and Spitzer observations Oesch et al. have identified a bright (M_UV ≈ -22) star-forming galaxy candidate at z ≈ 11. The presence of GN-z11 implies a number density ∼10^-6 Mpc^-3, roughly an order of magnitude higher than the expected value based on extrapolations from lower redshift. Using the unprecedented volume and high resolution of the BLUETIDES cosmological hydrodynamical simulation, we study the population of luminous rare objects at z > 10. The luminosity function in BLUETIDES implies an enhanced number of massive galaxies, consistent with the observation of GN-z11. We find about 30 galaxies at M_UV ≈ -22 at z = 11 in the BLUETIDES volume, including a few objects about 1.5 mag brighter. The probability of observing GN-z11 in the volume probed by Oesch et al. is ∼13 per cent. The predicted properties of the rare bright galaxies at z = 11 in BLUETIDES closely match those inferred from the observations of GN-z11. BLUETIDES predicts a negligible contribution from faint AGN in the observed SED. The enormous increase in volume surveyed by WFIRST will provide observations of ∼1000 galaxies with M_UV < -22 beyond z = 11 out to z = 13.5.