Abstract: Galaxy clusters play an important role in understanding the formation of structure in the Universe and can be used to constrain cosmological parameters. Thousands of clusters are known in the nearby Universe, but few are confirmed at large distances. Remote clusters provide a view of the early Universe, and are important for studying galaxy evolution. Here, I describe a technique for finding distant clusters using bent, double-lobed radio galaxies. These radio sources are active galactic nuclei (AGN) that result from outflows of material surrounding supermassive black holes in the centers of massive galaxies. These outflows are typically bent as a result of the relative motion between the host galaxy and the surrounding hot gas that fills clusters. Using the Sloan Digital Sky Survey (SDSS) and the Faint Images of the Radio Sky at Twenty-centimeters ( FIRST ) survey, I determine the frequency with which bent radio sources are associated with rich galaxy clusters in the nearby Universe (z 0.5), as compared to non-bent radio sources. I find that 60% of bent radio sources are located in rich cluster environments, compared to 10 - 20% of non-bent radio sources. Therefore, bent radio sources are efficient tracers for clusters and are useful as beacons of clusters at large distances. Bent radio sources may achieve their morphologies through large-scale cluster mergers that set the intracluster medium (ICM) in motion. Using a suite of substructure tests, I determine the significance of optical substructure in clusters containing radio sources. I find no preference for substructure in clusters with bent double-lobed sources compared to other types of radio sources, indicating that bent sources will not necessarily preferentially select clusters undergoing recent large-scale mergers. Having established that bent radio sources efficiently locate clusters, I have obtained deep, follow-up observations at optical and near-infrared wavelengths to uncover associated distant cluster candidates. In addition, a large Spitzer Space Telescope survey is underway to observe all bent sources not detected in the SDSS. Follow-up observations reveal a large number of high-redshift candidates. Further study of these objects will lend insight into galaxy formation and evolution and feedback between an AGN and its environment at high-redshift for clusters with a range of masses.

Since the radio signature of our own Milky Way was detected in 1931, galaxies have been observed from ultra-high energy gamma rays to long wavelength radio waves, providing fundamental insights into their formation, evolution and structural components. Unveiling the secrets of some of the best-observed galaxies, this atlas contains over 250 full-color images spanning the whole electromagnetic spectrum. The accompanying text explains why we see the component stars, gas and dust through different radiation processes, and describes the telescopes and instruments used. This atlas is a valuable reference resource on galaxies for students seeking an overview of multiwavelength observations and what they tell us, and researchers needing detailed summaries of individual galaxies. An accompanying website, hosted by the author, contains slide shows of the galaxies covered in the book. This is available at www.cambridge.org/9780521620628.

Extragalactic radio sources are among the most unusual and spectacular objects in the universe, with sizes in excess of millions of light years, radiated energies over ten times those of normal galaxies, and a unique morphology. They reveal some of the most dramatic physical events ever seen and provide essential clues to the basic evolutionary tracks followed by all galaxies and groups of galaxies. In The Physics of Extragalactic Radio Sources, David De Young provides a clearly written overview of what is currently known about these objects. A unique feature of the book is De Young's emphasis on the physical processes associated with extragalactic radio sources: their evolution, their environment, and their use as probes to solve other astrophysical problems. He also makes extensive use of the large amount of data now available from observations at x-ray, optical, and radio wavelengths to illustrate his main points. The Physics of Extragalactic Radio Sources will be a comprehensive introduction to the field for graduate students and a useful summary for astrophysicists.

In the centre of a cluster of galaxies lies a giant elliptical galaxy, dominating the others in terms of size and mass. This galaxy is called the Brightest Cluster Galaxy (BCG). Due to its privileged position near the gravitational potential well of the cluster, the BCG often hosts an actively accreting supermassive black hole. By releasing a tremendous amount of energy, this Active Galactic Nucleus (AGN) prevents the intracluster medium from cooling and condensing onto the BCG. This AGN feedback tends to quench star formation in BCGs. However, the way AGN feedback operates in primitive BCGs is not well understood. Moreover, recent studies seem to indicate that high redshift BCGs have a significant amount of in-situ star formation. One of those stabursting BCGs is in the cluster SpARCS104922.6+564032.5 (shortened into SpARCS1049). It forms stars at a rate of 950 ± 100 M☉ yr−1 and has a morphology reminiscent of a major gas-rich merger. In this dissertation, I will present multiwavelength radio observations of SpARCS1049 obtained with the Very Large Array (VLA), focusing on its BCG. I found three unresolved radio sources in SpARCS1049, including the BCG. The compact morphology of the radio emission from the BCG, as well as its good alignment with the galaxy optical centre, suggests that the radio emission originates from the AGN and not from star formation. However, the radio spectral energy distribution (SED) of this source is too poorly constrained to definitely determine its origin. Assuming all the radio emission of the BCG comes from its AGN, I found that the level of radio activity is comparable to the average activity of lower redshift BCGs. This was unexpected because a previous study found an immense cold molecular gas reservoir of 1.1 ± 0.1 × 10^11 M☉ in the centre of SpARCS1049, suggesting that something partially prevents the infalling of the gas into the black hole. I computed a new SED (from optical to radio) with my new radio flux measurements. I found that the bulk of the star formation probably takes place in the vicinity of the BCG but not inside. Since the star formation does not seem to be detected at radio wavelengths, we computed an upper limit on it and used this limit in combination with far infrared fluxes estimated from the SED to explore the extent of the star formation. I discovered that the star formation is probably very diffuse. Finally, I explored three formation scenarios that could explain the unusual infrared morphology of the BCG and the presence of a substantial molecular gas reservoir, using radio data (and non-detections) to constrain them: 1) a major gas-rich merger, 2) gas stripping from several small galaxies or 3) a displaced cooling flow. I found that the major gas-rich merger scenario is unlikely, but more data are needed to favor one of the two remaining scenarios.

The huge amount of data obtained by surveys in all wavebands, from radio to X-rays, has allowed major progress in the understanding of Active Galactic Nuclei and of their cosmic evolution. This book contains the proceedings of a conference intended to give a broad overview of the recent results obtained by recent AGN surveys over the whole electromagnetic spectrum. Topics which were discussed during the conference and are included in this volume are: AGN evolution, contribution to the cosmic background, AGN luminosity functions in different wavebands, multiwavelength properties of AGN, unified model and unconventional AGN, connection with the host galaxies, co-evolution of AGN and galaxies, implications for the local density of supermassive black holes. Future AGN surveys planned with forthcoming new observational facilities are also included.The proceedings have been selected for coverage in: ? Index to Scientific & Technical Proceedings? (ISTP? / ISI Proceedings)? Index to Scientific & Technical Proceedings (ISTP CDROM version / ISI Proceedings)? CC Proceedings ? Engineering & Physical Sciences