Thursday

In recent years, Herschel observations of the Galactic interstellar medium has revealed the ubiquity of dusty filamentary structures. In some clouds, filaments are organised in hubs, i.e. small networks of converging filaments. Understanding the link between the evolution of these hub systems and the formation of cores/stars inside them is at the heart of current star formation research. We have mapped the density and kinematic structure of SDC13, a 1000Msun filament hub system of 4 parsec-long filaments 3.6kpc away in the galactic plane, with the JVLA and GBT in NH3(1,1) and NH3(2,2) emission lines, probing 0.07pc scales with our high angular resolution of 3.3’’.
We find large scale kinematic differentiation between the filaments, along with smaller scale radial and longitudinal velocity gradients. Furthermore, we find the gas velocity dispersion is mostly sub-sonic in the diffuse parts of the filaments and becomes super-sonic towards (starless) cores. The three most massive cores are located at filament junctions, and on average, all identified cores are regularly spaced along the filaments, typical by 0.4pc, suggesting gravitational instabilities of these super-critical filaments are responsible for their fragmentation.
Altogether, we present a scenario for the evolution of SDC13 in which filaments first form as post-turbulent-shock structures where gas is mostly subsonic, then gravity takes over and starts shaping the evolution of the hub, both fragmenting filaments and pulling gas towards the centre of the gravitational well. Doing so, gravitational energy is converted to kinetic energy in both local (cores) and global (hub centre) potential well minima.