H [CSC]i[/CSC] Shells in the Large Magellanic Cloud

Abstract

A recent high-resolution H I survey of the Large Magellanic Cloud(LMC) shows that the structure of the neutral atomic interstellargas is dominated by numerous shells and holes, as well as complexfilamentary and spiral-type structure. We present an up-to-date catalogof candidate H I supergiant and giant shells in the LMC. The candidatesare visually selected from the H I data cube using selection andclassification criteria that are described. Twenty-three supergiantshells, defined as those regions whose extent is much larger thanthe H I scale height, are cataloged; 103 giant shells (radii lessthan the scale height of the H I gas) are cataloged. We further classifythe H I shells into five different types, based on the comparisonof the H I with their associated H{α} emission. For this purpose,we obtained new wide-field H{α} images of the LMC with a CCDcamera mounted on a 16 inch (0.41 m) telescope at Siding Spring Observatory.The pixel size of 20'' and the field of view of 12 deg are well matchedto the H I survey. The size distribution of H I shells follows acrude power law, N(logR)~R^{-1.5}. For constant energy inputto the H I shells and a constant shell creation rate, a shell luminosityspectrum of the form {\phis}(L)~L^{-β}, where {β}=1.75+/-0.2,is obtained. This agrees well with the observed H II region luminosityspectrum for the LMC of Kennicut, Edgar, {\amp} Hodge, which has{β}=1.75+/-0.15. H I shells containing H II regions and OBassociations seem to expand more rapidly than those without, providingdirect evidence for substantial input of mechanical energy from regionsof star formation.