Introduction to the Section on Galaxies

The Part XII, “Galaxies” of the Handbook of X-ray and Gamma-Ray Astrophysics reviews the impact of high-resolution X-ray observations on the study of galaxies and their evolution. Five chapters of the section discuss the main aspects of these studies: populations of X-ray binaries and hot interstellar medium, X-ray diagnostics of hot halos around isolated massive galaxies and predictions from modern structure formation simulations, studies of circumgalactic medium by using X-ray absorption lines, and high-resolution Chandra studies of the interaction between AGN and the surrounding ISM. The goal of these introductory notes is to place the following discussion into the broader astrophysical context.