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 likeCanal!

No good theory yet!

n vs Height from Galactic Midplane

Ferrière 2001, Rev.Mod.Phys. 73, 1031H2 gas

ionized gas

HI gas

average number density 　 n cm-3

Vertical (Quasi-)Hydrostatic Equilibrium?

PCR > Pmag > Pgas Parker Instability?

Pgas

Ferrière 2001, Rev.Mod.Phys. 73, 1031

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

（ 10-2 yr-1 ）（ 106 yr ）（ 100pc ） 3 = 1010 pc3 VGal.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) Tb=5K (bright) → 12.5K (dark)

Image : 60m dust emissionContour : 12CO(1-0) @ vLSR=-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 regionHI 21cm emission @ vLSR=-39.8 km/s

: Tb=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 (arXiv1101.2029) on “Dark Gas”

contour : 60μm dust emission

Radiative Equilibrium

WNM(Warm Medium)

CNM(Cold Medium)

Solid: NH=1019cm-2, Dashed: 1020cm-2

Radiative Cooling & HeatingSolid: Cooling, Dashed: Heating

Koyama & Inutsuka (2000) ApJ 532, 980 , based on Wolfire et al. 1995

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

20 p

c104*104 pixels

10,0002

Hennebelle & Audit 07

Audit & Hennebelle 20073D simulations12003

Heitsch et al. 40962

2D

Property of "Turbulence"

v < CS,WNM Kolmogorov-like SpectrumHennebelle & Audit 2007

Property of "Turbulence"

v < CS,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

condensationevaporation

Analytic Formula

Nagashima, Koyama, Inutsuka & 2005, MNRAS 361, L25Nagashima, Inutsuka, & Koyama 2006, ApJL 652, L41

Evaporation Timescale

Size of CNM cloud

CNM

WNM

Rc

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

Rc

Summary• Shock waves in ISM create

Turbulent CNM embedded in WNM.• In Turbulent Multi-Phase ISM

– Thermal Instability, Magnetic Field, Ambipolar Diffusion, etc.

What nextTurbulent Diffusion of Magnetic FieldParticle AccelerationOverall Modeling of Gaseous Galactic Halo

Good Information from CMB observations