Observational tracers of cluster evolution

• Main Author: Husband, Catriona
• Published: University of Bristol 2015
• Subjects: 523.1
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.683905

Galaxy clusters are the largest gravitationally bound structures in the Universe. Thought to form through a process of hierarchical merging, exactly how and when they form, and what happens to the galaxies within these dense environments, is still to be determined. At high redshifts we can find dense regions of space that we expect will evolve into a galaxy cluster by the present day but finding these regions, known as protoclusters, is difficult. Finding protoclusters is the main aim of this thesis and Chapters 3, 5 and 6 detail searches for protoclusters around quasars, sub-millimetre galaxies and radio galaxies, finding evidence that radio galaxies lie in the densest environments and sub-millimetre galaxies in the least dense on average. The protoclusters found are compared to simulations such as the Millennium Simulation in order to predict their eventual fate. The properties of the galaxies within these dense environments are also explored with reference to galaxies in the field, and in particular Chapter 4 presents a study of one interacting quasar system at z = 3.2 in detail. However, to fully understand galaxy and cluster evolution we must study both the high redshift protoclusters, and the highest redshift, virialised galaxy clusters, exploring how galaxy clusters continue to grow and evolve once they have formed and how these dense environments affect the galaxies within them. In Chapter 7 I present a sample of such high red shift galaxy clusters and explore their X-ray and infrared properties. This thesis reviews the work I have done over the last three and half years on the subject of galaxy clusters and protoclusters, starting with high redshift protoclusters and looking at the next 6 billion years of cluster evolution through the subsequent chapters.