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This book consists of invited reviews written by world-renowned experts on the subject of the outskirts of galaxies, an upcoming field which has been understudied so far. These regions are faint and hard to observe, yet hide a tremendous amount of information on the origin and early evolution of galaxies. They thus allow astronomers to address some of the most topical problems, such as gaseous and satellite accretion, radial migration, and merging. The book is published in conjunction with the celebration of the end of the four-year DAGAL project, an EU-funded initial training network, and with a major international conference on the topic held in March 2016 in Toledo. It thus reflects not only the views of the experts, but also the scientific discussions and progress achieved during the project and the meeting. The reviews in the book describe the most modern observations of the outer regions of our own Galaxy, and of galaxies in the local and high-redshift Universe. They tackle disks, haloes, streams, and accretion as observed through deep imaging and spectroscopy, and guide the reader through the various formation and evolution scenarios for galaxies. The reviews focus on the major open questions in the field, and explore how they can be tackled in the future. This book provides a unique entry point into the field for graduate students and non-specialists, and serves as a reference work for researchers in this exciting new field.

This prize-winning thesis deals with the observation and modeling of the spectral evolution of blazars. Based on single-dish light curves, a model of shock-shock interaction is tested and confirmed using multi-frequency high resolution Very Long Baseline Observations. He presents state-of-the art numerical relativistic hydrodynamic simulations and the corresponding non-thermal emission is calculated (eRHD simulations).The author further presents new analysis techniques for VLBI observations that can be applied to numerous sources and provide reliable results including an error estimate using Monte Carlo simulations. He also develops an analytical shock model that can be applied quickly to other single dish observations. He shows how novel techniques of extraction of physical parameters from observations can be applied to other astrophysical sources and provide a link to a better understanding of the physical mechanism operating in blazar jets.

I remember sitting spellbound, watching the movie When Worlds Collide. Two planets hurled through space toward Earth while scientists and engineers frantically raced to complete a rocket­ ship that would take them to safety. In the final moments the spaceship lifted off as the occupants watched the Earth bulge, crack, then literally explode as one of the planets struck it. As I left the theater I wondered if it was really possible for another world to collide with Earth. Later I learned that while many catastrophic collisions no doubt occurred early in the his­ tory of the solar system, today they are exceedingly rare. I was relieved, but in another sense I was disappointed (not that I hoped a collision of this type would actually occur). A collision of two objects in space, say, two stars, I was sure would be a spectacular event. It is quite unlikely, however, that we will ever witness the collision of two stars. The event is just too rare. But collisions of systems of stars-galaxies-oddly enough, are relatively com­ mon. In fact, we see evidence of several in the sky right now.

John Dyson has contributed to the study of the hydrodynamic processes that govern a wide variety of astrophysical sources which he has helped explain. In this volume dedicated to him, introductory reviews to a number of the key processes and to the sources themselves are given by leading experts. The mechanisms in which the multi-component natures of media affect their dynamics receive particular attention, but the roles of hydromagnetic effects are also highlighted. The importance of cosmic ray moderation and mass transfer between different thermal phases for cosmic ray moderation and mass transfer between different thermal phases for the evolution of flows are amongst the topics treated. The main types of regions considered include those where stars form, the circumstellar environments of evolved stars, the larger scale interstellar structures caused by the mass loss of stars, and those where the lines of AGNs form. The reviews complement one another and together provide a coherent introduction to the astrophysics of diffuse sources suitable for postgraduate students and researchers in astrophysics. Individual reviews stand alone and are suitable for an audience that includes advanced undergraduates doing final year projects.