Preprint typeset using LATEX style emulateapj v. 08/13/06 FORMATION OF MASSIVE MOLECULAR CLOUD CORES BY A CLOUD-CLOUD COLLISION

Recent observations of molecular clouds around rich massive star clusters including NGC3603, Westerlund 2 and M20 revealed that formation of massive stars can be triggered by a cloud-cloud collision. By using three-dimensional, isothermal, magnetohydrodynamics simulations with the effect of self-gravity, we show that massive, gravitationally unstable, molecular cloud cores are formed behind the strong shock waves induced by the cloud-cloud collision. We find that the massive molecular cloud cores have large effective Jeans mass owing to the enhancement of magnetic field strength by shock compression and turbulence in the compressed layer. Our results predict that massive molecular cloud cores formed by the cloud-cloud collision are filamentary and threaded by magnetic fields perpendicularly to the filament. Subject headings: stars: formation — instabilities — magnetic fields — shock waves 1