speaker: Alessio Traficante

From filaments to clumps: multi-scale dynamics in 70 micron quiet star-forming regions


The star formation mechanism occurs in well defined structures that can be identified and studied in great details in our own Galaxy: the process starts in giant molecular clouds, objects extended up to several tens of parsecs, within which elongated sub-structures, called filaments, may form. Inside filaments, round-like condensations extended up to ~1pc in radius, the so-called clumps, are the natural birth site of the pre- and proto- stellar cores, inside which will origin the future stars.
There are still many open questions in this hierarchical view of the star formation process: are these structures relatively confined from each other? Or is the large-scale environment affecting the dynamics of the formation down to clumps and cores? Is there a continuous interplay of the various forces involved in the process, namely turbulence, gravity and magnetic fields, at all scales? Or is there a relevant scale at which gravity will start to dominate the collapse, with critical implications on the star-formation mechanism?
After a general overview of the problem, I will present in details some recent results focused on the interplay between gravity and turbulence at the filament and clump scales. To investigate this interplay we have combined the dynamics of so-called 70 micron quiet clumps, i.e. very pristine regions not yet strongly affected by feedbacks, with the dynamics of the parent filaments in which they are embedded. Both clumps and filaments physical properties have been extracted from the Herschel survey of the Galactic Plane, Hi-GAL. The kinematics of filaments have been taken from ancillary CO data, while the kinematics of clumps has been studied with dedicated surveys carried out with the IRAM 30m telescope and aimed to observe high-density tracers such as N2H+ (1-0) an HCO+ (1-0). We observe a continuous interplay between turbulence and gravity, where the former creates structures at all scales and the latter takes the lead above a critical value of the surface density is reached, ~ 0.1 g cm^-2. In the densest filaments this transition can occur at the parsec, or even larger scales, leading to a global, gravitationally driven collapse of the whole region and to the formation of the most massive objects in the Galaxy.