Ultra Diffuse Galaxies (UDGs) were first identified using the Dragonfly Telescope Array in 2015. Their extreme properties (of low surface brightness, large size, and in some cases rich globular cluster systems) continue to present challenges for standard cosmological simulations. UDGs may represent galaxies with a range of properties: from puffed-up dwarfs to failed galaxies, from those with overly massive dark matter halos to some that are dark matter free. In my talk I will present new observations of UDGs from the Keck telescope, and also the Italian-led VEGAS (imaging from the VST) and LEWIS (data from MUSE) projects. These data will be contrasted with the latest simulations, summarising our current understanding of this extreme class of galaxy.
Marco Gullieuszik
