The Structure of the Inner Eastern Spiral Arm of M83

The spatial distributions of dust, Hβ, and nonthermal radio emission are studied in the inner eastern arm of M83 (NGC 5236) using VLA 20 cm continuum radio observations, a pure Hβ image, and a red continuum CCD image. Contrary to the case in, e.g., M51 and M101, the radio continuum emission in the neighborhood of the giant H II complexes is dominantly nonthermal. Nonthermal radio emission is also found to correspond well with the dust lanes, especially in the bar near the nucleus where the radio continuum is bright and the dust lanes are nearly perpendicular to the galaxy rotation. However, farther out along the eastern spiral arm, this dust-lane component of the nonthermal radio continuum fades, becoming overshadowed by a parallel ridge of strong nonthermal emission located well outside the dust lanes and following the general locus of the H II regions