http://arxiv.org/abs/1510.04742
The compressibility of molecular cloud (MC) turbulence plays a crucial role in star formation models, because it controls the amplitude and distribution of density fluctuations. The relation between the compressive ratio (the ratio of powers in compressive and solenoidal motions) and the statistics of turbulence has been studied systematically only in idealized simulations with random external forces. In this work, we analyze a simulation of large-scale turbulence(250 pc) driven by supernova (SN) explosions that has been shown to yield realistic MC properties. We demonstrate that SN driving results in MC turbulence that is only mildly compressive, with the turbulent ratio of compressive to solenoidal modes ~0.3 on average, lower than the equilibrium value of 0.5 found in the inertial range of isothermal simulations with random solenoidal driving. We also find that the compressibility of the turbulence is not noticeably affected by gravity, nor is the mean cloud expansion or contraction velocity (MCs do not collapse as a whole even if their own prestellar cores collapse to form stars). Furthermore, the clouds follow the same relation between the rms density and the rms velocity as in isothermal turbulence and their average gas density PDF is described well by a lognormal distribution, with the addition of a high-density power-law tail when self-gravity is included.
L. Pan, P. Padoan, T. Haugbolle, et. al.
Mon, 19 Oct 15
16/44
Comments: 5 pages, 4 figures, submitted to ApJL