Observations of giant bubbles in the Large Magellanic Cloud

Forbidden line S II/H-alpha intensity line ratio mapping and radial velocity data as well as monochromatic photographs are presented for a sample of bubbles in the LMC and some classical H II regions. The bubbles of unknown origin have line ratios greater than those of the H II regions and thus appear to fill the gap between thermal and nonthermal radio sources. All the bubbles or filamentary nebulae have important internal kinematical motions while the velocity dispersion is about 6-7 km/s for the H II regions. The large complex nebulae have values similar to simple H II regions in their brightest parts, while the faintest parts exhibit greater dispersions and conspicuous splittings and broadenings. The ionized bubbles appear to be intermediate between classical young H II regions and supernova remnants.