Dark matter in spiral galaxies: the mass of their stellar disks

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Spiral galaxies are immersed in vast halos of dark matter which make up more than 90% of their mass. The densities of the dark halos reflect the density of the expanding universe at the time when the halos condensed. The gravitational field of spirals and the density of the halos are measured from their rotation curves. For this analysis, the mass of their visible disks must be known, but it has not been possible to measure disk masses reliably until now. This project aims to exploit new instruments and improved analysis techniques to measure disk masses and halo densities accurately for the first time, and then to answer a central question of cosmology: when did galaxies of different masses form from the ancient expanding universe?