UMR 5672

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Formation and Evolution of Molecular Clouds: Gravity or Turbulence?

Mordecai Mac Low (American Museum of Natural History & Flatiron Institute)
When Jun 21, 2019
from 11:00 AM to 12:00 PM
Where Amphi F
Attendees Mordecai Mac Low
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The formation of molecular clouds from the turbulent, magnetized, diffuse interstellar medium and their subsequent evolution determines how star formation starts and proceeds. Magnetic support or turbulent pressure equilibrium were long argued to explain low observed star formation efficiencies in clouds. I present kiloparsec-scale, well-resolved, MHD simulations of the stratified, supernova-driven, interstellar medium performed with the Flash code, zooming in to reach resolutions of less than 0.1 pc within dense clouds. I use the results of these simulations to argue that gravitational collapse rather than any sort of turbulent equilibrium determines the dynamics of molecular clouds, with a focus on the relationships between size, velocity dispersion, and surface density of the clouds. It appears that Larson’s size-velocity relation may have both turbulent and gravitational origins in different regimes. We recover magnetic field strengths comparable to observed values. However, these fields are unable to prevent the densest regions from gravitationally collapsing, although they do appear to dominate the dynamics in the moderate density cloud envelopes, as shown by an analysis of gradient orientation. We conclude that molecular clouds are dynamically collapsing objects whose low star formation efficiencies likely come primarily from internal feedback leading to fast cloud destruction. I will end with preliminary results from cluster formation models done with the AMUSE framework to couple MHD and N-body computations in order to directly follow that feedback.

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