The formation and evolution of dense filaments and ridges

We confront two rather different star forming filaments: The Musca filament which forms isolated low-mass stars and the DR21 ridge which forms massive star clusters. Both regions are observed with several spectral lines, using the APEX, NANTEN2, IRAM 30m and SOFIA telescopes, that trace the gas from the ambient cloud into the dense filament/ridge. For both regions we find that the large scale kinematics are most likely explained by bending of the magnetic field which drives continuous inflow to the formed filament. For the DR21 ridge, it is additionally found that gravitational collapse takes over at a distance of $\sim$1-2 pc from the ridge. The bending of the magnetic field in both sources would be the result of a large scale collision that initiates star formation in both regions.