Mon. Not. R. Astron. Soc., 469, 383-393 (2017/July-3)
On the effective turbulence driving mode of molecular clouds formed in disc galaxies.
JIN K., SALIM D.M., FEDERRATH C., TASKER E.J., HABE A. and KAINULAINEN J.T.
Abstract (from CDS):
We determine the physical properties and turbulence driving mode of molecular clouds formed in numerical simulations of a Milky Way-type disc galaxy with parsec-scale resolution. The clouds form through gravitational fragmentation of the gas, leading to average values for mass, radii and velocity dispersion in good agreement with observations of Milky Way clouds. The driving parameter (b) for the turbulence within each cloud is characterized by the ratio of the density contrast (σρ/ρ0_) to the average Mach number ( M) within the cloud, b=σρ/ρ0_/ M. As shown in previous works, b ∼ 1/3 indicates solenoidal (divergence-free) driving and b ∼ 1 indicates compressive (curl-free) driving. We find that the average b value of all the clouds formed in the simulations has a lower limit of b > 0.2. Importantly, we find that b has a broad distribution, covering values from purely solenoidal to purely compressive driving. Tracking the evolution of individual clouds reveals that the b value for each cloud does not vary significantly over their lifetime. Finally, we perform a resolution study with minimum cell sizes of 8, 4, 2 and 1 pc and find that the average b value increases with increasing resolution. Therefore, we conclude that our measured b values are strictly lower limits and that a resolution better than 1 pc is required for convergence. However, regardless of the resolution, we find that b varies by factors of a few in all cases, which means that the effective driving mode alters significantly from cloud to cloud.
© 2017 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society
hydrodynamics - turbulence - methods: numerical - ISM: clouds - ISM: clouds
View the reference in ADS
To bookmark this query, right click on this link: simbad:2017MNRAS.469..383J and select 'bookmark this link' or equivalent in the popup menu