Galaxy Formation & Evolution: Observation, Measurement & Evidence

A modern galaxy includes stars, cold and hot gas, dust, a central black hole in many cases, and an extended dark-matter halo. These components exchange mass, energy, and angular momentum while the galaxy interacts with the circumgalactic and intergalactic environments.

Deep observations show that distant young galaxies are generally smaller, more irregular, and more actively star-forming than present-day massive systems. Simulations that combine gravity, hydrodynamics, cooling, star formation, and feedback reproduce many observed population trends.

Dark-matter overdensities collapse first and provide gravitational wells. Gas falls in, cools, forms stars, and can be expelled or heated by supernovae and active galactic nuclei. Mergers rearrange stellar orbits and gas, while fresh cosmic inflow can sustain later star formation.

Deep surveys compare galaxy size, color, mass, morphology, and star-formation rate across redshift. Simulations test whether the same physical prescriptions reproduce these evolving populations.