Galaxies and quasars in the epoch of reionization

The discovery of hundreds of star-forming galaxies and dozens of luminous quasars at z~6 indicates the presence of large stellar population of 1e11 Msun, supermassive black holes of ~109 Msun, and ultra-luminous infrared galaxies with LFIR ≥ 1012 Lsun when the Universe was less than one billion years old. These frontier observations present several challenges for theoretical models. I'll present modelings of the formation, evolution, and multi-band properties of these objects in the cosmic dawn, by combining multi-scale cosmological /hydrodynamic simulations with multi-wavelength radiative transfer calculations. Our models show that massive galaxies form early in the overdense regions, and that luminous quasars as those observed at z~6 can form through hierarchical galaxy mergers in the LCDM cosmology. These luminous, high-z quasars evolve from a starburst to a quasar phase, and are highly clustered. Their multi-band luminosity functions differ from those of galaxies at the same epoch. Large HII regions produced by stars already take place before major quasar phase, suggesting that galaxies may play a more important role in reionization than AGNs.