Triggered Star Formation on Galactic Scales

Abstract

Star formation in the turbulent ISM may be triggered by the collapse of an expanding sheet driven by stellar winds, stellar radiation and supernova explosions. The collapse produces clumps, some of which are gravitationally bound. In the low density environment of the galactic disks, clumps have masses in the range 10³-10⁶ M⊙ and they form if 1) the disk gas surface density is high enough, 2) the disk rotation is slow enough and 3) the gas cooling is fast enough. In the high density environment of molecular clouds, masses of fragments are in the range 1 - 100 M⊙. The mass spectrum can be approximated by a power law with the spectral index close to -2.3. We also introduce a model of the star forming factory, where a compact stellar cluster results from the collapse of an ISM giant cloud.