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Takashi Hosokawa ( NAOJ )

Dynamical Triggering of Molecular Cloud Formation around Expanding HII Region and PDR. Takashi Hosokawa ( NAOJ ). Shu-ichiro Inutsuka (Kyoto). Hosokawa & Inutsuka, astro-ph/0605648. also see, Hosokawa & Inutsuka, 2005, ApJ, 623, 917 2006, ApJ, 646, 240

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Takashi Hosokawa ( NAOJ )

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  1. Dynamical Triggering of Molecular Cloud Formation around Expanding HII Region and PDR Takashi Hosokawa ( NAOJ ) Shu-ichiro Inutsuka (Kyoto) Hosokawa & Inutsuka, astro-ph/0605648 also see, Hosokawa & Inutsuka, 2005, ApJ, 623, 917 2006, ApJ, 646, 240 2006, ApJ, 648L,131 Hosokawa, 2006, A&A, in press 2006.11.2 EANAM06 @ Daejeon, Korea

  2. CO Radiative Feedback for Molecular Cloud • Ionizing photons ( ) • Dissociating photons • ( ) Negative Feedback destroy molecular cloud and suppress star formation ( H2 → HI →HII ) NGC3603 by HST (e.g., Whitworth 1979 ) V.S Positive Feedback shock front sweeps up H2 gas to trigger star formation ( compression of H2 ) (e.g., Elmegreen & Lada 1977) Sh104 ; Deharveng et al. (2003)

  3. Radiative Feedback for diffuse ISM W5 Negative Feedback Photoionization of the neutral medium : promising process to supply the diffuse warm ionized medium. ( HI →HII ) (e.g., Miller & Cox 1993 ) Wisconsin H-alpha Mapper (WHAM) ; Haffner et al. (2003) V.S Positive Feedback Shock front sweeps up the ambient neutral medium. Reformation of molecules is triggered in the compressed layer. CO HII ( HI →H2 ) (e.g., Koyama & Inutsuka 2000 ) 33pc Karr & Martin (2003)

  4. Motivation THIS TALK Hosokawa & Inutsuka, 2005, ApJ, 623, 917 2006, ApJ, 646, 246 etc. HI HI H2 (2) Expanding HII regions trigger the star formation and/or destroy the molecular cloud (3) HII region expands in the diffuse neutral medium (1) HII regions expand in the molecular clouds In phases ( 3 ) , what is the role of HII regions expanding in the neutral medium? 1.photoionization (HI→HII)2. reformation of molecules (HI→H2) Which is more efficient? Does the molecular formation occur?

  5. Basic Equations 1D Radiation-Hydrodynamics Calculation hydrodynamics : 2nd-order Godunov method continuity： momentum eq. ： 17 processes energy eq. ： equation of state ： Radiative transfer ： UV photon ( ) FUV photon ( ) freq. Dependent chemistry： H+/H, O+/O, H/H2, C+/CO (Nelson & Langer 1998) (Photoinization) (photodissociation)

  6. Situation Shell Shock front Cold Neutral Medium ( n~10/cc, T~100K ) Ionization front • Study the physical/chemical structure of the shell • Does molecular gas form from ambient neutral medium?

  7. Dynamical Evolution Central star：41Msun , ambient medium：CNM (n=10/cc) ( equilibrium state with typical FUV field ) Snapshots Temperature Density 5Myr 3Myr t=1Myr 7Myr 9Myr Initial T Dense and cold shell is formed around the HII region density : n~1000/cc, temperature: T~30 K

  8. Accumulation of Molecules nH2/nH nCO/nHZC M-S life time Shock front Ionization Front H2 are formed in the shell, but CO are hardly formed : Dark H2 Intermediate gas phase between neutral medium and molecular clouds

  9. Hunt of Predicted Gas Phase Hunt the cold (T~a few ×10 K) HI HI 21cm line emission HI Self-Absorption (HISA)： absorption of colder HI against the emission by the warmer HI (Tb ~100 K) Canadian Galactic Plane Survey CGPS ; Taylor et al. (2003) • galactic plane survey @ radio, IR • angular resolution : about 1‘ • distribution of HI, HII, CO, dust Channel Map Blue image:21cm emission, Red contour:CO

  10. CGPS data in W5 HII region 21cm continuum (HII gas) Tb=5K (bright) → 12.5K (dark) Image : 60μm dust emission Contour : 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.

  11. CGPS data in W5 HII region HI 21cm emission @ vLSR=-39.8 km/s : Tb=45K (bright) → 110K (dark) contour : 60μm dust emission • Shell-like HISA feature is found around W5 HII region. • HISA feature overlaps with the dust shell.

  12. Summary We have studied the role of the HII region expanding in the diffuse neutral medium. • Numerical Calculation (in CNM) • Cold (T~30K) and dense (n~1000/cc) shell is formed around HII region. • H2 is formed in the shell, but CO is hardly formed. • intermediate gas phase between the diffuse neutral medium and • molecular clouds • Analysis with CGPS data ( in W5 HII region ) • Shell-like HISA feature is found around ionized gas. • The dust shell shows goodcorrelation with the shell-like HISA. • Distribution of CO molecules showpoor correlation with both • dust shell and HISA.

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