Kinetic and Structural Evolution of Self-gravitating, Magnetized Clouds: 2.5-Dimensional Simulations of Decaying Turbulence

摘要: The molecular component of the Galaxy is comprised turbulent, magnetized clouds, many which are self-gravitating and form stars. To develop an understanding how these clouds' kinetic structural evolution may depend on their level turbulence, mean magnetization, degree self-gravity, we perform a survey direct numerical MHD simulations in three parameters independently varied. Our consist solutions to time-dependent equations two-dimensional grid with periodic boundary conditions; additional "half" dimension also incorporated as dependent variables third Cartesian direction. Two our parameters, magnetization parameter β≡c2sound/v2Alfven Jeans number nJ≡Lcloud/LJeans, allow us model clouds that either meet or fail conditions for magneto-Jeans stability magnetic criticality. parameter, sonic Mach ≡σvelocity/csound, allows initiate turbulence sub- super-Alfvenic amplitude; employ isothermal equation state throughout. We evaluate times each cloud become gravitationally bound measure model's energy loss over fluid-flow crossing time. compare density field morphology quantify differences contrast generated by internal stresses models differing magnetization. find values β nJ, but not initial , determine time gravitational binding collapse: nH2=100 cm-3, unmagnetized collapse after ~5 Myr, magnetically supercritical generally 5-10 Myr (although smallest stable survive until t~15 Myr), while subcritical remain uncollapsed entire simulations; scale tg∝n−½H2. find, contrary some previous expectations, less than factor 2 difference between turbulent decay varying strength; maximum time, B~14 μG 1.4 flow tcross=L/σvelocity (or 8 typical giant parameters). In all amplification strength up at least βpert≡c2sound/δv2Alfven=0.1, 25% 60% one non-self-gravitating stages evolution, when have =5-10, mass-averaged magnitudes log(ρ/) range 0.2-0.5, increasing both toward low high β. Although conclusions about statistics be affected assumption, note only more strongly appear consistent estimates clump/interclump contrasts inferred Galactic clouds.