10.1098/rsta.2002.1062 The resolved history of galaxy evolution By Jarle Brinchmann Max-Planck-Institut f¨ ur Astrophysik, Karl-Schwarzschild-Str. 1, 85478 Garching bei M¨ unchen, Germany Published online 24 October 2002 We briefly review the study of the evolution of galaxies from an observational point of view, with particular emphasis on the role of the Hubble Space Telescope in probing the evolution of the different morphological types of galaxy. We show how using the stellar mass of galaxies as a tracer of evolution can improve our understanding of the physical process taking place before turning our eyes towards the future and giving an overview of what we can expect from future advances in technology. Keywords: galaxy evolution; fundamental parameters of galaxies; stellar content of galaxies 1. Introduction In some ways astronomy has been a science with a focus on resolving objects and phenomena, be it Galileo resolving the Milky Way into a myriad of stars or Fraun- hofer resolving absorption lines in the spectrum of the Sun or radio astronomers detecting rapid temporal variations in the radio emission of pulsars. These advances have led to many great discoveries, such as the structure of our own Galaxy and the physical nature of the Sun. The improvements in resolution continue to have an impact in many diverse areas of astronomy, and it would prove too long-winded to examine all these here; instead we will focus only on the area of galaxy evolution. In particular, we will almost exclusively focus on the impact of improved spatial resolution, and in this context the importance of the Hubble Space Telescope (HST) cannot be neglected; most of the discussion will be devoted to the advances made with the help of this beautiful instrument. In recent years, however, significant progress has been made in improving resolution with ground-based telescopes, and in the future these may reach and even overtake the resolving power of space-based telescopes. We will return to this topic later in the discussion when we look towards the future, where we will also discuss advances in spectral and temporal resolution. First, however, let us introduce the study of galaxy evolution, which will be the dominant theme of this paper. Galaxies are the biggest well-defined units of the Universe, and understanding their formation and evolution has long been a major goal for researchers. The current theoretical understanding is that the matter content of the Universe is dominated by dark matter which only interacts through gravity. This dark matter has structure on very small scales, and these small-scale structures collapse and force baryons to follow. Stars, and later galaxies, form within these One contribution of 20 to a Triennial Issue ‘Astronomy and Earth science’. Phil. Trans. R. Soc. Lond. A (2002) 360, 2711–2723 2711 c  2002 The Royal Society