Troels Haugbolle - April 20, 2017

Supernova feedback and the influence on star formation and molecular cloud structure

Turbulence is ubiquitous in molecular clouds, but its origin is still unclear
because molecular clouds are usually assumed to live longer than the turbulence
dissipation time. A likely origin of interstellar medium turbulence is supernova
explosions. I will present recent simulations with a volume of (250 pc)^3,
specifically designed to test if supernova driving alone can be responsible for
the observed turbulence inside molecular clouds. We find that supernova driving
establishes a velocity scaling consistent with the usual scaling laws of
supersonic turbulence and that the statistics of the molecular clouds selected
from our simulation is consistent with that of observed clouds from the
Outer-Galaxy Survey, the largest molecular cloud sample available.
To investigate the effect of feedback we compute the star formation rate that
originate ab initio due to supernova-driven turbulence. Because of the large
number of well-resolved clouds with self-consistent boundary and initial
conditions, we obtain a large range of cloud physical parameters with realistic
statistical distributions, and an unprecedented sample of star-forming regions
to test star formation rate models and to interpret observational surveys. We
confirm the dependence of the star formation rate per free-fall time on the
virial parameter found in previous small scale simulations. We find that the
star formation rate per free-fall time in molecular clouds can take any value
in the range 0 to 0.2, and its probability distribution peaks at a value ~0.025,
consistent with observations. The size and scatter in the star formation per
free-fall time versus viral parameter relation are consistent with recent
measurements in nearby molecular clouds and in clouds near the Galactic center.