Final Report Summary - ESSOG (Extracting science from surveys of our Galaxy)
Techniques were developed for the extraction of science from surveys of our Galaxy undertaken both from the ground and from space, in preparation for the release of data from the European Space Agency's 'Cornerstone Project' Gaia, which since 2014 has been monitoring the motions of over a billion stars. The first goal is a dynamical model of the distributiions of stars, dark-matter and interstellar gas. The longer term aim is to establish how our prototypical Galaxy was assembled. We developed a new way of making model galaxies in which stars of different types cohabit with each other and dark-matter particles and interstellar gas in the gravitational field that they jointly generate. Software was released that enables groups with less dynamical expertise to build their own models. We developed a new technique for checking the validity of distances to stars, and, using this technque, uncovered systematic errors in published distances, which in one case had led to a qualitatively incorrect picture of our Galaxy's stellar halo. Application of our model-building machinery to data from an international spectroscopic survey conducted from Australia led to the strongest constraints on the distribution of our Galaxy's dark matter. From a suite of 100 precision simulations of the gradual accumulation of stars within a pre-existing dark halo we gained important insights into galaxy assemly. Giant molecular clouds play a crucial role early in a galaxy's life by scattering stars. They delay the formation of the bar and may prevent the bar thickening into a bulge before the current epoch. The level of radial migration observed in these simulations agrees almost perfectly with that inferred from the degree of chemical inhomgeneity of the solar neighbourhood.