Download Dynamical Triggering of the Star / Molecular Cloud Formation

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
Radiative Feedback for Molecular Cloud
• Ionizing photons (
• Dissociating photons
(
Negative Feedback
destroy molecular cloud and
suppress star formation
NGC3603 by HST
( H2 → HI → HII )
(e.g., Whitworth 1979 )
CO
V.S
Positive Feedback
shock front sweeps up H2 gas
to trigger star formation
( compression of H2 )
Sh104 ; Deharveng et al. (2003)
(e.g., Elmegreen & Lada 1977)
)
)
Radiative Feedback for diffuse ISM
Negative Feedback
Photoionization of the neutral medium
: promising process to supply
the diffuse warm ionized medium.
( HI → HII )
Wisconsin H-alpha Mapper (WHAM) ; Haffner et al. (2003)
(e.g., Miller & Cox 1993 )
V.S
W5
Positive Feedback
CO
HII
Shock front sweeps up the ambient neutral
medium. Reformation of molecules is
triggered in the compressed layer.
( HI → H2 )
(e.g., Koyama & Inutsuka 2000 )
33pc
Karr & Martin (2003)
Motivation
Hosokawa & Inutsuka, 2005, ApJ, 623, 917
2006, ApJ, 646, 246 etc.
THIS TALK
HI
HI
H2
(2) Expanding HII regions trigger
(3) HII region expands in the
(1) HII regions expand in the
the star formation and/or destroy
diffuse neutral medium
molecular clouds
the molecular cloud
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?
Basic Equations
1D Radiation-Hydrodynamics Calculation
hydrodynamics : 2nd-order Godunov method
continuity：
momentum eq. ：
17 processes
energy eq. ：
equation of state ：
Radiative
UV photon (
transfer ：
) FUV photon (
freq. Dependent
chemistry： H+/H, O+/O, H/H2, C+/CO (Nelson & Langer 1998)
(Photoinization)
(photodissociation)
)
Situation
Shell
Cold Neutral Medium
( n~10/cc, T~100K )
Shock front
Ionization front
• Study the physical/chemical structure of the shell
• Does molecular gas form from ambient neutral medium?
Dynamical Evolution
Central star：41Msun , ambient medium：CNM (n=10/cc)
( equilibrium state with typical FUV field )
Temperature
Snapshots
Density
t=1Myr
3Myr
5Myr 7Myr 9Myr
Initial T
Dense and cold shell is formed around the HII region
density : n~1000/cc, temperature: T~30 K
Accumulation of Molecules
M-S life time
nCO/nHZC
nH2/nH
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
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
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.
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.
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 good correlation with the shell-like HISA.
• Distribution of CO molecules show poor correlation with both
dust shell and HISA.