Filamentary cold structure from colliding supershells

Supershells are large dense shocks, created by the combined stellar feedback from OB associations. The gas around the stars is compressed, forming a dense spherical shell which typically breaks up into molecular clouds. We have performed high resolution numerical simulations of this process, focusing on the fluid instabilities which affect the shock morphology before gravity has had time to act. In these simulations cold structures of typical sizes on the order of parsecs are formed out of the dense shock material in a variety of physical states. These clumps are organized in filaments with tens of parsecs lengths when a large-scale shear is present. In simulations where the flow of stellar material is followed with a tracer quantity cold structures practically do not contain any enriched material from the OB associations at the time of their creation.