A review of elliptical and disc galaxy structure, and modern scaling laws

TL;DR

This review comprehensively covers the historical and modern understanding of galaxy structures, including elliptical and disc galaxies, and discusses scaling laws that serve as benchmarks for galaxy evolution studies.

Contribution

It provides an extensive overview of galaxy structural components and modern scaling relations, highlighting their importance as benchmarks for evolutionary research.

Findings

Modern scaling relations are often curved.

Compact ellipticals at high redshift may be bulges of present-day disc galaxies.

Structural features like nuclear deficits and dark matter halos are key to understanding galaxy evolution.

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, discs and elliptical galaxies. The quantification of galaxy nuclei, such as central mass deficits and excess nuclear light, plus the structure of dark matter halos and cD galaxy envelopes, are discussed. Issues pertaining to spiral galaxies including dust, bulge-to-disc 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 modelling. 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 disc galaxies.