The Dynamic Nature of Baryons in Halos

The circumgalactic medium of typical galaxies represents a new frontier in the pursuit of a complete theory of galaxy formation. Understanding the nature and evolution of this material over cosmic time is a crucial element of galaxy formation theory, as it is the main source of fuel for star formation and is the material that is most sensitive to the ill-understood feedback processes that regulate galaxy growth. In contrast to the relatively quiescent baryons of the diffuse intergalactic medium, and those bound in the extreme environs of galaxy clusters, circumgalactic baryons are only now coming within observational grasp. Astronomers will soon have the opportunity to study the material that is infalling onto, or outflowing from typical galaxies.

The advancement of this field will require a broad multi-waveband approach, encompassing radio, millimetre, optical, UV and X-ray observations, in concert with targeted, state-of-the-art gasdynamical models of galaxy evolution. This workshop will bring together leading astronomers from this broad range of disciplines to converge on optimised, holistic approaches to key science drivers. Can multi-waveband probes provide a complete accounting of halo baryons over cosmic history? Can we observe and, with these data, assess the importance of cold and hot accretion modes in the growth of galaxies, as advocated by numerical simulations? What are the observable impacts of feedback processes, such as winds driven by supernovae and black holes, on halo baryons? Is the dynamical state of halo baryons (e.g. accreting, outflowing, or rotating) linked to galaxy morphology? Is the Milky Way a representative test case for observational programs?

The purpose of the this workshop is to unite observers of all relevant wavebands with theorists to identify synergies between established observational disciplines and those newly enabled by advances in instrumentation. The workshop format will emphasize interactive collaboration and discussion, in seeking to bring this emerging field to the forefront of galaxy formation research. Optimistically, the workshop will lead to a white paper articulating this subject as a central challenge in galaxy formation, highlighting the synergistic evolution of observational and theoretical studies. Ultimately, the workshop aims to grasp the interest of a new generation of scientists in this rapidly evolving field, and unite researchers in disparate astrophysical disciplines into new collaborations that might not otherwise develop.