Exploring the early evolution of galaxies

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Central to our understanding of the the Universe is the topic of galaxy evolution. The details of how these large systems of stars, gas, dust and dark matter formed and evolved from the near-uniform matter distribution created by the Big Bang impact on how the properties of the rest of the Universe evolved. While there are quite detailed theoretical ideas about how galaxies form which feed in to multiple different and often competing/contradicting models of galaxy formation, observational measurements of early galaxies that can be used to constrain and test these models are currently rare. Particularly important to testing these models are observations of galaxies seen when the Universe was young. The galaxies seen should be the comparatively primitive building blocks of the much more mature and bigger galaxies seen today. Given the limited time available for such systems to evolve, their evolution should not be particularly complex and consequently their properties should directly inform and test our understanding of the early stages of galaxy evolution. In the past few years we have made great progress in identifying distant galaxies through deep observations with the largest optical and near-infra-red sensitive telescopes. We have identified with certainty over 100 galaxies which are seen when the Universe was no older than about 1 billion years old ( it is now 13.7 billion years old), and have identified candidates for galaxies seen at even earlier times. We currently have little understanding of their properties in any detail, having concentrated on their discovery and measuring the simplest of their properties and statistics. Almost all of the information we have on these systems comes from their ongoing star formation episodes which result in strong UV emission from short-lived massive stars. The bulk of the matter in these systems, whether baryons (ordinary matter) or dark matter, is not bright or detectable in the rest-frame ultra violet. Consequently, we have little or no information on the bulk of the material in and around these galaxies, severely limiting their use to develop and test models of early galaxy evolution. A new generation of instrumentation is just becoming available, instruments that will transform our ability to explore the properties of the galaxies and their environments in some detail. Using KMOS, a multi-object near-IR spectrograph which will be available on the VLT, and ALMA and other mm/sub-mm wave telescopes, we will determine accurate redshifts, dynamics and masses for the galaxies, determine whether they contain an appreciable number of the first generation of stars (as yet undetected) and search for signs of any material infalling onto the galaxies as part of their evolution. We will probe the properties of cool and cold gas, both atomic and molecular, that must be within the galaxies and in their surroundings if they are going to go on to form the largest galaxies that we see in the Universe today. By combining the results of all of these observational studies along with existing data on the same galaxies, we will develop a much more complete picture of how early galaxy evolution proceeds, a picture that will directly inform and challenge models of the key processes that leads to the formation of galaxies like our own Milky Way.