Star-burst regions in the LMC

Aims. Filamentary structures of early type stars are found to be a common feature of the Magellanic Clouds formed at an age of about $0.9{-}2$ $\times$ $10^8~{\rm yr}$. As we go to younger ages these large structures appear fragmented and sooner or later form young clusters and associations. In the optical domain we have detected 56 such large structures of young objects, known as stellar complexes in the LMC for which we give coordinates and dimensions. We also investigate star formation activity and evolution of these stellar complexes and define the term “starburst region”. Methods. IR properties of these regions have been investigated using IRAS data. A colour–magnitude diagram (CMD) and a two-colour diagram from IRAS data of these regions ware compared with observations of starburst galaxies and cross-matching with HII regions and SNRs was made. Radio emission maps at 8.6-GHz and the CO ($1\rightarrow0$) line were also cross correlated with the map of the stellar complexes. Results. It has been found that nearly 1/3 of the stellar complexes are extremely active resembling the IR behaviour of starburst galaxies and HII regions. These stellar complexes illustrating such properties are called here “starburst regions”. They host an increased number of HII regions and SNRs. The main starburst tracers are their IR luminosity (F60 well above 5.4 Jy) and the 8.6-GHz radio emission. Finally the evolution of all stellar complexes is discussed based on the CO emission.