Dynamics of Multi-Phase Interstellar Medium Shu-ichiro Inutsuka (Nagoya Univ) Thanks to Hiroshi Koyama (Univ. Maryland) Tsuyoshi Inoue (Kyoto Univ.) Patrick Hennebelle (Paris Obs. & ENS) Masahiro Nagashima (Nagasaki Univ.) Keywords: radiative cooling/heating, thermal instability, MHD, ambipolar diffusion, etc.

Polarization Map of Synchrotron Rad Depolarized region looks like Canal! No good theory yet!

 n  vs Height from Galactic Midplane Ferrière 2001, Rev.Mod.Phys. 73, 1031 H 2 gas ionized gas HI gas average number density  n  cm -3

Vertical (Quasi-)Hydrostatic Equilibrium? P CR > P mag > P gas  Parker Instability? P gas Ferrière 2001, Rev.Mod.Phys. 73, 1031

HI vs H 2 (Radial Direction) 内側では分子雲ガスの質量が多い

Various Components (Radial) NGC6946 MRI does not explain this! equipartition assumed

M51 Synchrotron Polarization (Fletcher & Beck 2005)

Dynamical Timescale of ISM Dynamical Three Phase Medium –McKee & Ostriker 1977 SN Explosion Rate in Galaxy… 1/(100yr) Expansion Time… 1Myr Expansion Radius… 100pc （ yr -1 ）  （ 10 6 yr ）  （ 100pc ） 3 = pc 3  V Gal.Disk Dynamical Timescale of ISM  1Myr « Timescale of Galactic Density Wave  100Myr (10kpc) 2  100pc

CGPS data in W5 HII region 21cm continuum (HII gas) T b =5K (bright) → 12.5K (dark) Image : 60  m dust emission Contour : 12 v LSR =-39.8 km/s  Ionized gas is surrounded with the dust shell.  Distribution of CO molecules show poor correlation with the dust shell.

CGPS data in W5 HII region HI 21cm v LSR =-39.8 km/s : T b =45K (bright) → 110K (dark)  Shell-like HI Self-Absorption feature is found around W5.  HISA feature overlaps with the dust shell. Hosokawa & SI 2007, ApJ 664, 363 See also recent Planck paper (arXiv ) on “Dark Gas” contour : 60μm dust emission

Radiative Equilibrium WNM (Warm Medium) CNM(Cold Medium) Solid: N H =10 19 cm -2, Dashed: cm -2

Radiative Cooling & Heating Solid: Cooling, Dashed: Heating Koyama & Inutsuka (2000) ApJ 532, 980, based on Wolfire et al grains

2D Evolution from Unstable Equilibrium Periodic Box Evolution without Shock Driving With Cooling/Heating and Thermal Conduction Without Physical Viscosity  Pr = 0

1D Shock Propagation into WNM Density-Pressure Diagram Density-Temperature Diagram –through unstable region unstable Koyama & SI 2000, ApJ 532, 980 See also Hennebelle & Pérault 1999

1D Shock Propagation into CNM Density-Pressure Diagram Density-Temperature Diagram CNM becomes thermally unstable with shock. Koyama & Inutsuka 2000,ApJ 532,980 unstable

Shock Propagation into WNM Hot Medium Color: Density Koyama & Inutsuka, 2001 Ambient ISM WNM

20 pc 10 4 *10 4 pixels 10,000 2 Hennebelle & Audit 07 Audit & Hennebelle D simulations Heitsch et al D

Property of "Turbulence"  v < C S,WNM  Kolmogorov-like Spectrum Hennebelle & Audit 2007

Property of "Turbulence"  v < C S,WNM  Kolmogorov-like Spectrum Hennebelle & Audit 2007 Armstrong, Rickett, & Spangler 1995

Evaporation of Spherical CNM in WNM Smaller CNM cloud evaporates: R~0.01pc clouds evaporate in ~Myr condensation evaporation Analytic Formula Nagashima, Koyama, Inutsuka & 2005, MNRAS 361, L25 Nagashima, Inutsuka, & Koyama 2006, ApJL 652, L41 Evaporation Timescale Size of CNM cloud CNM WNM RcRc

Evaporation of Spherical CNM in WNM If the ambient pressure is larger, the critical size of the stable cloud is smaller. "Tiny Scale Atomic Structure"? Braun & Kanekar 2005 Nagashima, Inutsuka, & Koyama 2006, ApJL 652, L41 Ambient Pressure Critical Radius CNM WNM RcRc

Instability of Transition Layer important in maintaining the “turbulence” Cold Medium Warm Medium Evaporation Front Thickness

Instability of Transition Layer Similar Mechanisms… 1) Darrieus-Landau (DL) Instability Flame-Front Instability # Important in SNe Ia # Effect of Magnetic Field See Dursi (2004) 2) Corrugation Instability in MHD Slow Shock – Edelman 1990 – Stone & Edelman 1995 unburnedburned Flame Front Thickness

Linear Analysis of New Instability Growth Rate (Myr -1 ) Cold Medium Warm Medium Evaporation Front T 2 WNM CNM T 1 11 22 Field length wavenumber k y /2  pc   step function approx. isobaric approx. unstable Inoue, Inutsuka, & Koyama 2006, ApJ 652, 1131

Summary Shock waves in ISM create Turbulent CNM embedded in WNM. In Turbulent Multi-Phase ISM –Thermal Instability, Magnetic Field, Ambipolar Diffusion, etc. What next Turbulent Diffusion of Magnetic Field Particle Acceleration Overall Modeling of Gaseous Galactic Halo  Good Information from CMB observations