EPoS Contribution 
Support against gravity in magnetoturbulent gas
Wolfram Schmidt Institut für Astrophysik, Göttingen, Germany  
How do turbulence and magnetic fields affect the support of selfgravitating gas against collapse? A common approach is to apply a simple Jeans criterion, with turbulent and magnetic pressure terms added to the thermal pressure. Although this can be motivated from a generalization of the virial theorem for a turbulent magnetized cloud, it is purely tentative to infer the support of overdense regions within the cloud in this way. I will show how the dynamical equation for the divergence of the velocity field naturally leads to a completely general definition of thermal, turbulent, and magnetic support. This has already been applied to analyze the relative contributions to the support of the intergalactic medium in cosmological simulations by Zhu et al. (2010) and by Iapichino et al. (2011). In my presentation, I will generalize this approach to magnetohydrodynamical turbulence and I will statistically analyze the support of selfgravitating isothermal gas in AMR simulations performed by Kritsuk et al. (2011) and by Collins et al. (private communications). It turns out that there is no simple relation between the averaged support of the gas at a given overdensity and the magnitudes of the thermal, turbulent, and magnetic pressures, as suggested by the generalized virial theorem. Moreover, it appears that even in the case of high Mach numbers and strong magnetic fields, it is predominately the structure of the density field that is important for the support, albeit this structure is shaped by magnetohydrodynamical turbulence.  
Collaborators: David Collins, LANL, USA Alexei Kritsuk, UCSD, USA 
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