From clouds to fragments: on the multi-scale interplay between gravity and turbulence
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 fragments, 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 fragments? Is there a continuous interplay of the various
forces involved in the process, namely turbulence, gravity, 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, clump and fragment scales. To investigate this
interplay at the larger scales, 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. At smaller scales, I will discuss
the different scenarios of fragments formation in light of the most
recent results from the SQUALO (Star formation in QUiescent And Luminous
Objects) project. This ALMA survey has been designed to investigate the
formation properties in a sample of massive clumps selected to be at
various evolutionary stages and with the common feature that they are
all accreting at the clump scales. Our
results show that a large scales 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. At the same time, the
fragmentation properties show several indications that the fragment are
"clump-fed", i.e. the process is dynamical and the gravity dominates the
collapse inside our massive clumps.