Formation of the First Massive Galaxies in Cosmological Simulations and Their Observational Properties

We study the formation of the first massive galaxies and their observational properties for comparisons with JWST or ALMA data by performing cosmological radiative-hydrodynamics simulations. We find that galaxies in overdense regions have high star formation rates larger than ∼10 M_⊙ yr^-1 at z=10 and their stellar masses reach 10⁹ M_⊙. The star formation rates of our model galaxies at z≲12 nicely match recent JWST data. In addition, we show that the morphology of galaxies drastically changes with time via major mergers and stellar feedback.