Program: GS-2007B-Q-44

GALEX has discovered a population of spiral galaxies hosting extended UV ("XUV") disks that are dramatically larger than their optical extent. Such galaxies support star-formation at an unexpectedly high rate in locales previously thought to be dynamically stable. Indeed, XUV disks are populated with conspicuous UV-bright stellar complexes often lacking luminous, counterpart HII regions. We propose GMOS-S observations of PGC9103, one of the most extreme XUV disks known. Deep broadband imaging enables us to characterize the mass, age, and extinction of star-forming clumps at large radii. Multi-object spectroscopy will be used to measure nebular abundances and density throughout PGC9103's XUV disk. We will reassess the star formation law and gauge the importance of XUV disks relative to galaxy evolution.