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Published on October 9, 2007

Author: Heather

Source: authorstream.com

Slide1:  Turbulence and Magnetic Fields in the Large Scale Structure of the Universe Scales in Astrophysical and Laboratory Plsamas Turbulence and Magnetic Fields in LSS Dongsu Ryu (Chungnam National University, Korea) in collaboration with H. Kang, J. Kim & J. Cho Slide2:  MHD (magneto hydrodynamic) regime Scales in Astrophysical and Laboratory Plasmas plasma parameter >> 1 frequencies of phenomena << plasma frequency -> charge neutrality weakly coupled plasma regime Slide3:  for for and and (typical astrophysical environments) (typical laboratory environments) Slide4:  Fluid regime for the case that Coulomb collision is dominated for the case that particle-field interaction is dominated mean free-path for electron-proton relaxation gyro-radius of protons gyro-radius of elections mean free-path for electron-electron & proton-proton collisions collisionless fluid regime collisional fluid regime Slide5:  for (typical astrophysical environments) (typical laboratory environments) for in both cases 5 regimes collisionless fluid regime heat to proton heat to electron collisional fluid regime with collisional fluid regime with Slide6:  Plasma beta for (typical astrophysical plasmas) (typical laboratory plasmas) for magnetically dominated Slide7:  To simulate astrophysical plasmas in laboratory 1) 2) 3) tough to achieve in laboratory ! if then trivially achieved but other parameter ranges should have interesting implications to astrophysical and space plasmas! Turbulence in the Coma Cluster ICM:  Coma pressure map 145 kpc Turbulence in the Coma Cluster ICM (Schuecker et al. 2004) Slide9:  histogram of projected pressure fluctuations fluctuations are mostly adiabatic pressure fluctuations dr vs dT Slide10:  noise subtracted power spectrum of projected pressure fluctuations with slope n ~ -7/3 ... – 5/3 energy content of turbulence as fraction of thermal energy subsonic turbulent Close to Kolmogorov Slide11:  simulated RM maps assumed field strength decreasing radially assumed power spectrum with fixed slop n=3: scale-invariant n=11/3: Kolmogorov investigated the radial profiles of <RM> and sRM for different n (Murgia et al. 2004) Turbulence in RM Slide12:  - used RM in Abell 119 for comparison with simlation - n=2 is a good fit and Kolmogorov (n=11/3) does not reproduce the data comparison with obs. Slide13:  used RM’s for non-cooling flow clusters n = 1 – 2 provides the best fit to the data most of the magnetic field energy in the small scales field strength is a factor ~ 2 lower than assuming smallest RM scale for coherence length slope of power psectrum Slide14:  Turbulence in RM (Vogt & Ensslin 2005) RM map in Hydra North (cooling flows clusters), processed with Pacman Slide15:  power spectrum of magneitc field B ~ 6 mG lB ~ 3 kpc Kolmogorov Slide16:  Turbulence in clusters - Eturb < Eth - flat magnetic field spectrum or spectrum folded at large scale - no or weak cluster scale field (?) subsonic super-Alfvenic turbulence (?) magnetic field strength in clusters (?) turbulence outside clusters and in filaments and sheets (?) turbulence in ISM supersonic strong regular field (Goldreich & Sridhar model) with weak or no regular field and subsonic flow super-Alfvenic turbulence (Cho & Vishniac 2000) Slide17:  The large scale structure of the universe in simulation - L cold dark matter cosmology L = 0.73, DM = 0.27, gas = 0.043, h=0.7, n = 1, 8 = 0.8 without/with gas cooling - computational box: (100 h-1 Mpc)3 10243 cells for gas and gravity, 5123 DM particles (Ryu, Kang et al 2003, 2005) X-ray emissivity e = 10-37 – 10-29 erg cm-3 s-1 and higher gas temperature T = 104 - 108 K and higher Slide18:  (100 Mpc/h)2 2D slice shock waves rich, complex shock morphology: shocks “reveal” filaments and sheets (low density gas) X-ray emissivity cluster pancake filament (100 h-1 Mpc)2 2D slice Slide19:  velocity field and shocks in a cluster complex (25 h-1Mpc)2 2D slice Slide20:  distribution of shock Mach no. Slide21:  vorticity in a cluster complex (25 h-1Mpc)2 2D slice curl(v)|x log(|curl(v)|) 2000 kms-1 / 300 kpc 20 kms-1 / 1 Mpc 1500 kms-1 / 300 kpc -1500 kms-1 / 300 kpc Slide22:  vorticity in a filament 25 x 15.5 x 5 (h-1Mpc)3 box log(|curl(v)|) magenta: 600 kms-1 / 300 kpc yellow: 20 kms-1 / 1 Mpc Slide23:  preshock density postshock density preshock flow speed unit normal to shock surface curvature radius of shock surface Generation of vorticity at shocks Slide24:  rms vorticity inside structures (clusters, filaments, and sheets) wrms = ~ 500 kms-1/Mpc ~1/(2x109 yrs) rms vortivity in clusters/groups wrms ~ 1000 kms-1/Mpc ~ 1/(109 yrs) rms vortivity in filaments/groups wrms ~ 500 kms-1/Mpc ~ 1/(2x109 yrs) rms vorticity outside structures (voids) wrms = ~20 kms-1/Mpc ~1/(5x1010 yrs) produced mostly at shocks ? shocks are ubiquitous and process a large amount of energy! ~ a few x 0.1 keV/baryon (Ryu et al 2003, Kang et al 2005) Mach number distribution average distance btw shocks ~ 3 h-1 Mpc overall ~ 1 h-1 Mpc inside structures Slide25:  assumptions: vorticity cascades and develops into MHD turbulence and magnetic field is generated - Emag/Eturb is a function of t/tturn-over Magnetic field in the large scale structure of the universe v = vdiv + vcurl vdiv = div(f) vcurl = curl(c) Eturb = ½rvcurl2 tturn-over = 1/w w = curl(vcurl) Slide26:  Simulation of incompressible MHD turbulence with very weak regular field Emag ~ 2/3 Ekin at saturation t/tturn-over 20 40 60 80 tturn-over ~ 1/w Slide27:  t ~ tage in filamets t ~ tage in clusters t/tturn-over Emag/Eturb Slide28:  Eturb – Emag relation in the large scale structure of the universe Eturb (erg/cm3) Emag (erg/cm3) Emag = Eturb Slide29:  r – B relation in the large scale structure of the universe B (Gauss) rBM/<rBM> Slide30:  T – B relation in the large scale structure of the universe B (Gauss) T (K) Slide31:  intergalactic magnetic field along filaments (~18x27 Mpc)2 2D slice 1 Mpc = 3.26 x 106 light-years Slide32:  inside clusters, B > ~mG around clusters (T > 107 K), B ~ 0.1 mG in filaments (105 K < T < 107 K, or WHIM), B ~ 1 nG in sheets (104 K < T < 105 K, or lukewarm), B ~ 10-11 G in voids (T < 104 K), B ~ 10-13 G Medium is in the state of plasma even in the largest possible scales of the universe! Slide33:  - astrophysical plasmas are composed of thermal particles, cosmic ray particles, and magnetic fields - turbulent motion is ubiquitous in astrophysical plasmas - interactions among these components are important in understanding astrophysical plasma Slide34:  Thank you !

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