Formation of Structure in Molecular Clouds: A Case Study
  Molecular clouds (MCs) are highly structured and ``turbulent''. Colliding gas streams of atomic hydrogen have been suggested as a possible source of MCs, imprinting the filamentary structure as a consequence of dynamical and thermal instabilities. We present a 2D numerical analysis of MC formation via converging HI flows. Even with modest flow speeds and completely uniform inflows, non-linear density perturbations as possible precursors of MCs arise. Thus, we suggest that MCs are inevitably formed with substantial structure, e.g., strong density and velocity fluctuations, which provide the initial conditions for subsequent gravitational collapse and star formation in a variety of galactic and extragalactic environments. 
F. Heitsch (1,2), A. Burkert (1), L. Hartmann (3), A.D. Slyz (4),   J.E.G. Devriendt (5) ((1) University Observatory Munich,...