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Properties of the Structures formed by Parker - Jeans Instability

Properties of the Structures formed by Parker - Jeans Instability. Y.M. Seo 1 , S.S. Hong 1 , S.M. Lee 2 and J. Kim 3 1 ASTRONOMY, SEOUL NATIONAL UNIVERSITY 2 SUPERCOMPUTING CENTER , KiSTI 3 KOREA ASTRONOMY & SPACE SCIENCE INSTITUTE. Previous Works of Parker Instability.

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Properties of the Structures formed by Parker - Jeans Instability

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  1. Properties of the Structuresformed by Parker-Jeans Instability Y.M. Seo1, S.S. Hong1, S.M. Lee2 and J. Kim3 1 ASTRONOMY, SEOUL NATIONAL UNIVERSITY 2 SUPERCOMPUTING CENTER , KiSTI 3 KOREA ASTRONOMY & SPACE SCIENCE INSTITUTE

  2. Previous Works of Parker Instability Results Summary UnderUniform External Gravity → convective motion everywhere in the disk. UnderNon-uniform External Gravity [Kim & Hong 1998; Kim, et al. 2004] → ISM turned into thin sheets due to interchange mode UnderSelf-gravity [ Lee & Hong 2006, accepted ] → compatible with HI super-clouds, but not with GMCs. This work Isothermal, magnetized, and self gravitating disk under influence of external gravity

  3. Observations 1.Giant Molecular Cloud [Blitz 1993, PP III] 2x105 ~1x106 MSUN; ~50H2 cm-3 ; separation 0.4~0.6 Kpc Star forming rate →Gas consumption rate → Need about 33 Myrs [Larson 1994] 2. HI Super-cloud [Elmegreen & Elmegreen in 1981] 1x106 ~4x107MSUN ; ~10 H cm-3 ; separation 1~4 Kpc mean separation of 106Msun clouds 1.2Kpc [Alfaro, Cabrear-Cano, Delgado 1992] Arm Crossing time →about 120 Myrs - All HI super-cloudshaveGMCsinside ; not allGMCsare located insideHI super-clouds.

  4. Dispersion Relation : Undular Mode Self Gravity + External Gravity ΩJEANS< ΩPARKER Solar Neighborhood ΩJEANS≈ΩPARKER ΩJEANS> ΩPARKER

  5. Non Linear Simulations Code: Isothermal MHD TVD MHD + Poisson (Nx, Ny, Nz) = (256, 512, 256) → (1Kpc, 2Kpc, 1Kpc) , with 4pc pixel resolution o = 2mHcm-3,  = 0.3 , cs = 5.0 km/s H = 156pc , h = 0.94Kpc, b = 20, 15, 10 Time is in units of [H/cs] , which is 28.3 Myr. Cs is observed velocity dispersion of cloudlets.

  6. Cylinder-like structure perpendicular to (Parker Cylinder) Non Linear Simulations • ΩPARKER> ΩJEANS 78 Myrs after transient phase 210 Myrs after transient phase Azimuth Magnetic Field Radial

  7. Non-linear Simulations • ΩJEANS> ΩPARKER 170 Myrs after transient phase 130 Myrs after transient phase Azimuth Magnetic Field Radial Parker cylinders merge with each other. Parker cylinders form first.

  8. Fourier Analysis ΩPARKER> ΩJEANS ΩJEANS> ΩPARKER • ΩPARKER> ΩJEANS : Several peaks • λy ≈ 2 kpc → HI super-cloud scale structure • λy ≈ 705 pc, λy ≈ 445 pc → GMCs scale structure • ΩPARKER< ΩJEANS : A broad peak

  9. Properties of Clumps 93 Myrs after transient phase Azimuthal Magnetic Field Radial Clump Identification code [Jonathan P. Williams, Eugene J. De Geus, & Leo Blitz]

  10. Mass Distribution

  11. Mean Separation ΩParker> ΩJean Averaged distances between all of each clumps in three dimension Projected distance of the peaks → 500pc & 1140pc Mean density → a little lower than GMCs The clumps are precursors of GMCs Radius → a little larger than GMCs

  12. Properties of Clumps Parker instability dominates in the early stage of clump formation.

  13. Principle Axis of Clumps Total 22 Clumps at t = 9.8 Clumps are made by the Parker instability

  14. Energies of Clumps [unit in erg] Clumps are in the virial equilibrium. Surface energy ≈ Internal energy Cs is NOT thermal sound speed

  15. Kolmogorov’s slope : -5/3 Slope : -3 Slope: -5 Fourier Analysis

  16. Discussion & Summary 1. Structures & Formation Time Scales ΩPARKER > ΩJEANS →Formation of HI superclouds scale structures and GMCs scale structures within 130Myrs Parker cylinders and GMCs form first. This Work HI super-clouds Parker cylinder & GMCs Fragmentation Collect Parker cylinder and GMCs GMCs & HI super-clouds GMCs in HI-superclouds 2. Parker - Jeans instability tends to steepen the power spectrum.

  17. Initial Equilibrium Configuration • (1 + ) cs2 ism(z) = - ism(z) tot ►2 ism = 4G ism(z), ext = tot-ism • ism(z) = osech2 (z/ H) sech2b (z/ h) ► o= 2mHcm-3,  = 0.3, cs = 5.0 km/s H = 156pc, b = 20, h = 0.94Kpc • In Simulations ► b = 20, 15, 10 The other parameters are fixed.

  18. Observational Facts tot  [Bienayme, Robin, & Creze 1987, A.Ap., 180, 94.] ρ  [Boulares, A. & Cox, D.P. 1990, ApJ, 365, 544.] B = 4 ±1 μG(local regular field)  [Rainer Beck, 2001, Sp Rev. 99: 243-260]

  19. Synthesized HI Profiles • < σV(x,y,z) >x,y ≈ 5.0 km/s BUT FWHM ≈ 2.5 km/s < Cs • → Clump velocity is much too small compared to observed cloud velocity.

  20. Time vs < Vx(x,y,z) >xy /Cs Time vs < σVx(x,y,z) >xy /Cs Cs = 5.0 km/s < Vx(z) > ≈ 0.0 km/s < σVx(z) > ≈ 5.0 km/s

  21. Slop :0.75

  22. Magnetic to Gas Pressure Velocity dispersion of cloudlets ,

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