Subventions et des contributions :

Subvention ou bourse octroyée s'appliquant à plus d'un exercice financier. (2017-2018 à 2022-2023)

The Lambda Cold Dark Matter (ΛCDM) "standard" model is remarkably successful in matching cosmological observations on spatial scales larger than about 1 Mpc. But when astronomers look on smaller scales -- i.e., on the scales of galaxies and galaxy clusters -- a number of problems emerge. The predictions of the model disagree with the observed numbers of low-mass galaxies in the local universe, the measured central mass distributions in those galaxies, and the dynamical masses of the Milky Way's brightest companions. Understanding these discrepancies has become a top priority for the international astrophysics community, and the last 5-10 years has seen significant progress on both the observational and theoretical fronts.

In terms of theory, a new generation of hydrodynamical simulations having high dynamic range and high mass resolution, and employing increasingly sophisticated treatments of the physical processes that are believed to be important for galaxy formation, are being brought to bear on the problem. Observationally, new instruments and telescopes are being used to study the faintest and lowest-mass stellar systems, as these objects provide especially stringent tests of the models. This scrutiny has already produced some surprises: e.g., the existence of some exceptionally diffuse galaxies in cluster environments; large numbers of dense nuclei (some of which contain super-massive black holes) at the centres of intermediate- and low-mass galaxies; thin stellar streams in the Galactic halo that trace the remains of disrupted galaxies; rich populations of star clusters found in a diversity of environments whose numbers appear to scale in proportion to dark matter mass; and an ever-increasing number of "ultra faint" dwarf galaxies in the Milky Way that appear to be the most dark matter dominated systems in the universe.

Over the past decade, I have been a founder, or co-founder, of some of the largest observing programs ever to use the local universe as a testing ground for cosmological models of structure formation. State-of-the-art UV/optical/IR imaging -- mainly from the Canada-France-Hawaii Telescope and the Hubble Space Telescope -- are being used, along with spectroscopy from 4-10m-class telescopes, to explore the properties of the stellar systems in two complementary environments: the Virgo Cluster, the nearest rich cluster of galaxies, and the halo of the Milky Way. My graduate students, whose continued support would be made possible with this grant, are leading two key elements of this program: (1) characterizing the total masses (including black hole content), star formation histories and chemical enrichment histories of galactic nuclei and establishing their connection to other types of compact stellar systems; and (2) using white dwarfs, blue horizontal branch stars and metal-poor stars to explore the stellar populations, structure and evolution of the halo and disk.