Mousumi Das (Indian Institute of Astrophysics)
It is well known that galaxy disks are embedded in massive dark matter halos which make their disks more stable against global disk instabilities. However, there may also be significant amounts of dark matter in galaxy disks as well, as indicated in the early studies of the vertical motion stars in our Galaxy. The disk dark matter is especially important for late type spiral galaxies that have extended neutral hydrogen (HI) gas disks, as it may provide the vertical support for the gas disk. In this talk I will present a method for determining the disk dark matter based on measurements of the HI velocity dispersion in face-on galaxies and then apply it to estimate the disk dark matter in the nearby galaxy NGC628. I will also discuss how the disk dark matter plays a role in supporting star formation in the outer disks of galaxies, as in extended UV (XUV) galaxies and disk galaxies that have ongoing cold gas accretion. Some recent UV observations of star formation in the halo dominated regions of galaxies will also be presented.