Galaxy Formation in ΛCDM Cosmology

This is a golden age for galaxy formation: Existing and especially new telescopes are providing observations that challenge and illuminate rapidly improving theory and simulations. This review describes the formation of the cosmic web and the structure of the dark matter halos that provide the scaffolding of the Universe. It then summarizes how empirical models, semianalytic models, and hydrodynamic simulations attempt to account for key properties of the galaxy population, including the main sequence of star-forming galaxies, the inefficiency of star formation, the shape evolution and color bimodality of galaxies, and the phenomena that cause galaxies to quench their star formation. It concludes with a summary of observations that have challenged the cosmological constant cold dark matter (ΛCDM) paradigm of galaxy formation—including the Hubble and S 8 tensions, bright galaxies in the early Universe, an extragalactic background light mystery, missing satellite galaxies, the diversity of dwarf galaxies, the cusp–core problem, the too-big-to-fail problem, stellar clumps, planes of satellite galaxies, and galaxies without dark matter—and solutions that have been proposed.