Towards a Cosmological View of Disk Galaxy Structure

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The broadly-accepted cosmological model for the composition and evolution of the Universe explains a remarkable range of astronomical observations. However, it is not yet clear how galaxies form and evolve within this framework, and understanding how this process happens is one of the biggest challenges in cosmology today. Detailed observations of the galaxies around our own provide important clues to the processes that create their internal structure. Spiral galaxies similar to the Milky Way are particularly useful in this regard, because their properties can be inferred from the distributions and orbital speeds of gas and stars in their disks. Detailed structural studies of nearby spiral galaxies therefore provide key evidence that allows astronomers to decipher the physics of galaxy formation and evolution. Early comparisons between the measured structure of spiral galaxies and simple theoretical predictions found that the two were strongly discrepant. Astronomers now suspect that this disagreement arises not from a failure of cosmology, but from overlooked details of how galaxies form. It is now clear that gas and stars can alter dark matter halos during galaxy formation more efficiently than previously thought, and that the subtle interplay between different galactic components after they have formed can also drive galaxy evolution.While several plausible mechanisms have been invoked to explain the observed structure of nearby galaxies, it is not yet clear which of them are generic during galaxy formation. Proof-of-concept comparisons between detailed cosmological simulations and handfuls of observed galaxies have been successful, but population-wide galaxy studies are still lacking. This is due in part to a dearth of high-quality orbital speed maps for nearby galaxies required for these careful comparisons. This will change in the near future with the advent of large spectroscopic surveys at different wavelengths. At the same time, the size and efficiency of modern telescopes enable exquisitely detailed studies of individual galaxies. The next few years are therefore exciting ones for galaxy formation research, since it will be possible to systematically test proposed theories for the first time. The main objective of my research is to understand the structure of nearby spiral galaxies in a cosmological context. My research group carries out systematic structural studies of large galaxy samples using software that we have developed for this purpose. The physicality and robustness of our code are unparallelled, and our group is therefore poised to constrain the dark and luminous matter contents of thousands of nearby spiral galaxies from forthcoming surveys. My group also devises and carries out novel experiments on extreme or unique systems in the local Universe, in order to gain insight into the physics of the galaxy population as a whole. My program provides a collaborative, world-class training environment in which highly qualified personnel excel.Canada is an international leader in astronomy, often ranking first in this field: this success engenders technology and innovation that give our country a competitive edge on the world stage. My program addresses some of the key questions that drive astronomical research: how are dark matter halos altered when spiral galaxies form within them? How do the orbits of the stars and gas in spiral galaxies drive their evolution? Is the observed structure of spiral galaxies consistent with cosmological predictions when these processes are taken into account? What is the nature of the dark matter? My work will help answer these questions, making progress towards my field's ultimate goal of developing a complete theory of cosmological galaxy formation and evolution.