Molecular Clouds in the Supergiant Shell LMC 4: Evidence for Triggered Cluster Formation

Abstract

We have completed fully sampled observations of CO (J=1-0) towardthe supergiant shell (SGS) LMC 4 at a linear resolution of 40 pcwith NANTEN. The result is the discovery of 18 clumpy CO clouds,17 of which well delineate the SGS traced by H{α} and H I.The remaining one cloud inside the SGS exhibits a cometary shapewith an H I tail heading toward the center of the SGS. A comparisonbetween the CO clouds and the young stars, including H II regionsand stellar clusters, indicates that all the associated young starsare on the side of the clouds facing toward the center of the SGS.The typical separation between the cloud peaks and young stars is~40-100 pc. These facts strongly suggest that star formation hasbeen triggered by the expanding shell that is driven by OB stars,indicating the important role of SGSs in cluster formation in theLMC.