Obtaining turbulence properties from surveys Jungyeon Cho Chungnam

Obtaining turbulence properties from surveys Jungyeon Cho Chungnam National University, Korea Cho & Ryu (2009, Ap. JL) Cho et al. (2013, in prep. )

ISM is in turbulent state

Molecular Clouds: DV ~ a few km/sec Observed line width > thermal line width Turbulence

Electron density spectrum Big power law (WIM): Armstrong & Spangler (1995) Slope ~ -5/3 pc AU

HI cloud (SMC) : Stanimirovic+(1999) HI column density power-law spectrum

Important turbulence properties -Driving scale -Density fluctuation (sr) -…

Density PDF • Numerical studies (for example, VS 94, PN 97, PN 99, Passot and VS 98, E. Ostriker et al. 01) showed that density PDFs of isothermal (gamma=1), turbulent flows follow a log-normal distribution. for a mass-conserving system Slide from J. Kim (modified)

1 D isothermal HD (Passot & Vazquez-Semadeni 94)

3 D isothermal HD (Nordlund & Padoan 1999)

3 D isothermal MHD (Ostriker+ 2001)

We observe projected quantities (e. g. S, …) Question: Can we obtain sr? Density (MHD) To observer S=projected r

PPV cube Intensity V v 2 useful observables Itot S Centroid

Column density of turbulence

Velocity centroids (Mach=2. 3, Alfven Mach=0. 7) This last expression valid for optically thin media, w/emissivity proportional to density (e. g. cold HI) From A. Esquivel

dr>0 dr<0 s. S . . . ~ ~l|dr| l=? ? ? 1/2 (L/l) lsr 1/2 (L/l)

Cho & Ryu (2009) showed that l ~ Lint, where Lint is the integral scale k 2 ES(k) FT k 1 s. S ~ Lintsr (L/Lint)1/2 k~1/l

Lint= s. S ~ Lintsr (L/Lint 1/2 )

Conclusions -If we observe optically thin line emissions, we can get 1. Driving scale 2. sr 3….