Recent Star Formation in the Extreme Outer Disk of M83

Ultraviolet imaging with the Galaxy Evolution Explorer (GALEX) has revealed an extensive sample of UV-bright stellar complexes in the extreme outer disk of M83, extending to about 4 times the radius at which the majority of H II regions are detected (R = 5.′1, or 6.6 kpc). These sources are typically associated with large-scale filamentary H I structures in the warped outer disk of M83 and are distributed beyond the galactocentric radii at which molecular interstellar medium has yet been detected. We present measured properties of these stellar complexes, including far-UV and near-UV magnitudes and local gas surface density. Only a subset of the outer-disk UV sources have corresponding H II regions detected in Hα imaging, consistent with a sample of mixed age in which some sources are a few megayears old and others are much more evolved (~108 yr).