Elliptical and disk galaxy structure and modern scaling laws

Abstract

A century ago, in 1911 and 1913, Plummer and then Reynolds introduced their models to describe the radial distribution of stars in “nebulae.”� This article reviews the progress since then, providing both an historical perspective and a contemporary review of the stellar structure of bulges, disks, and elliptical galaxies. The quantification of galaxy nuclei, such as central mass deficits and excess nuclear light, plus, briefly, the structure of dark matter halos and cD galaxy envelopes, are discussed. Issues pertaining to spiral galaxies including dust, bulge-to-disk ratios, bulgeless galaxies, bars, and the identification of pseudobulges are also reviewed. An array of modern scaling relations involving sizes, luminosities, surface brightnesses, and stellar concentrations are presented, many of which are shown to be curved. These “redshift zero” relations not only quantify the behavior and nature of galaxies in the Universe today but are the modern benchmark for evolutionary studies of galaxies, whether based on observations, N-body simulations, or semi-analytical modeling. For example, it is shown that some of the recently discovered compact elliptical galaxies at 1. 5 < z < 2. 5 may be the bulges of modern disk galaxies.