大質量星・巨大星団の形成の謎を解く

14!-,• $)2; ,23 7:%>1"329#8/*9-.15<=532/0-6'• 4 (<=;+:• ?Bonnell 2002@• <=4?Krumholtz+ 2009@352/0&2&2

Radiation pressure barrier in high-mass star formation• Very strong radiationpressure at the dust
destruction front
Lam pressure (ρv2)> radiation pressure(L/4πr2c)

Hosokawa et al. 20103

O stars and formation mechanismn Stars having more than 20 M
n Staller wind, strong UV, SNe, etc..
However, it is not known
how the O stars are formed?
n Observational issues- few, distant from us etc..
n Theoretical issues- large mass accretion rate etc.
~ 10−4–10−3 M/yr[~10−6 M/yr for low-mass stars]

We need some triggering mechanisms

Wolfire & Cassinelli (1986)!;%32• *.9!E 29":$>C+H8( :9B)@6/B35 8<FG<:9673=,• ; -FG#E0C• *"&+-)1DA;'E4C(Fukui, Torii, Inoue+ 2009-2019,more than 30 papers)
;:?
•5

Numerical simulations of Cloud-Cloud Collisions
Step 1

Step 2

Step 3

Habe & Ohta 92

Anathpindika+12

-6.0 - -5.1 km/s

-5.1 - -4.1 km/s

-4.1 - -3.1 km/s

-3.1 - -2.2 km/s

-2.2 - -1.2 km/s

-1.2 - -0.2 km/s

-0.2 - 0.7 km/s

0.7 - 1.7 km/s

K km/s
0.0

4.0

8.0

Y [pc]

50-50

10
X [pc]

157

RCW120 (Spizter bubble S7)• A Spitzer bubble member• d ~ 1.3 kpc (Rodgers+1960)• Beautiful ring-like emission
at 8 micron enclosing
ionized gas.
• An exciting O8 star
• Expanding HII region? (e.g.,Zavagno+2010)

Green : 8um
Red: 24um
Blue : Hα: exciting star
○ : Class Ⅰ△: Class Ⅱ

8Cloud-cloud collision (Torii+ 15)

0.1Myr9

CCC triggers formation of massive dense core
MHD simulations

Inoue and Fukui 201310

Numerical simulations of Cloud-Cloud Collisions

Inoue & Fukui 13, ApJLSuper Star Cluster Westerlund 2n (l, b) = (284°.27, -0 °.33)
n O-Star x 12, WR-star x 2
n Total mass of the stars 4,500 M
(Rauw+07)
n Age 2−3 Myr (Piatti+98)
n Distribution of dust influenced
by stars (Churchwell+98)
n Star formation in progress
n YSO ~300 (Whitney+04)

We found two giant molecular clouds(GMCs) associated with Westerlund 2(Furukawa+09; Ohama+10)

SSC Westerlund 2 (Furukawa+09; Ohama+10)

Furukawa+09

n Two GMCs (red/blue) are complementary distributed toward Westerlund2.
n The velocity separation of the two clouds is 15–25 km s−1,
can not be bound with the gravity.

Spitzer image

RCW38• 巨大星団 RCW38

Wolk et al. 2006

• 距離: ~ 1.7kpc• 励起星: O5.5型 (IRS2)• O型星候補: ~20個
VLT image• 銀河系でもっとも若い巨大星団（~0.1Myr）(Fukui+16; Wolk+06)• 赤外線の明るいリッジ
構造 IRS1• 中心部1pcに豊富なガス

14

RCW38 (Fukui+ 16)• CO J=1-0, 3-2輝線観測• 速度差12km/sの2つ分子雲– Ring cloud (Blue-shifted), Finger cloud (Red-shifted)• 2つの分子雲を速度上で結ぶbridge feature (Haworth+15a,b)• 分子雲衝突15

RCW3816

ALMA Cycle-3 7m+TP Observations• 2015.1.01134 (PI Fukui)• Band 6 - 7m(7 pointings) + TP– 12CO, 13CO, and C18O (J=2-1),
SiO (J=5-4), H30α, Continuum• Band 7 - 7m(14 pointings) + TP
– 13CO and C18O (J=2-1), CS(J=7-6),
Continuum• Spatial resolutions– Band 6: ~ 7” x 5” (~0.050pc)– Band 7: ~ 5” x 3.5” (~0.035pc)• Velocity resolution: ~0.2 km/s
• Final r.m.s:– Lines:~0.2 Jy/beam– Continuum: ~0.03 Jy/beam17

Core A, B  (Torii+ 19)
 341GHz
FWHM(C18O)~ 3.7km/s

Core A

Core B

FWHM(C18O)~ 3.9km/s• 2つのコアの方向で片側20–50km/sのbipolar outflow

18

19

20

21  (Enokiya+ 2019)no OB stars
1 ≤ number of OB stars < 10
number of OB stars ≥ 10

Relative velocity [km/s]

100

Sgr B2
Star Burst

Loop 1 & 2

10Sgr A
Super Star Cluster
Cluster

1

Slope: 0.26 ± 0.056
Intercepts: -5.08 ± 1.28
21102223

24

101010Column density [cm-2]

25

1022

Parametern0Value
300 cm-3Δn/n00.33

B020 μG

Vcoll

10 kms-1

Resolution(8.0/512) pc

23

24

25

The cavity

Radius
1.5 pcCollision
compressed layer

LengthInitialmass

4 pc 500Msol

Averagedensity columndensity

300 cm-311021 cm-2

3000 cm-3

11022 cm-2

Collision Thickness Current
radiusmass
1.5 pc1 pc 1000 Msol

26

27

The Large Magellanic Cloud: LMC• Distance: ~ 50 kpc(one of the nearest)• Metallicity: ~1/2 Z◉• Active star formation• Massive star formation• young populous clusters
高空間分解能での観測が可能

R136

28

RMC 136 (R136)

スーパースタークラスター- 年齢が若い : ~ 1.5 Myr- 局部銀河群で最大の星団 : ~105 M◉- 超大質量の星が存在
265 M◉ , 195 M◉, 175 M◉, 135 M◉ の星が存在 (Crowther et al. 2010)

銀河間潮汐相互作用による巨大星団形成の可能性
K. Bekki and M. Chiba

SMC-0.82-0.82 Gyr

-0.27

-0.27 GyrFujimoto & Noguchi 1990
潮汐相互作用による巨大星団形成を示唆.
• ~ 0.2 Gyr 前 LMC 
SMC が近接遭遇

LMC-0.1400-0.14 Gyr• LMC のガスの攪乱

Bekki & Chiba 2007aX-axis

X-axis30

O/WR star formation of the whole LMC• Total number ofO/WR stars ~ 700(SAGE Meixner etal. 2006)• O –type star ~ 600• WR star ~ 100

HI Ridge

N44• We analyzed 20 star
forming regions• ~ 560 O/WR stars
are possibly formedby the collision ofHI flows caused byinteraction
About 80% of O/WR stars of the LMC were tidal
between the SMC
possibly formed by tidally-driven colliding and LMC.

HI flows at least.

× : O-type star: WR star 31

Collision of two HI components (Fukui+ 17)

位置速度図(a)AB lineRA : 86.69 - 87.41oK0(15D

Declination (J2000)

Lo-68
-68-72o

コントア: L, イメージ: D

-72

-100

-50
0
Voffset [km s-1]

5032-1

Collision of two HI components (Fukui+ )9 Co
1.



2.  I 1 kpcIL

DR136 ブリッジ構造LコントアCOI D

"   L
!# DFukui, Tsuge et al. 2017, Tsuge et al. 2019-5033

相対速度[km s-1]

Schematic diagram of the collision
NorthSouthBridge
R136

Low velocity
componentLine of sight←Diskat present~ 3Myrs ago

Scenario of the R136 formation (+ around massive stars)
Tidal interaction between the LMC and SMC 0.2 Gyr ago=> Collision of HI flow => massive star formation

34

35

Formation of massive star clusters
Superstar Clusters

Westerlund 2 (MW)Totalstellar mass

104MR136 (the LMC)

<r105M

B1 (Antennae Galaxies)<106-7M

Staller wind, strong UV, SNe, etc..
=> Significant influence on the interstellar medium.

It is important to understandthe evolution of matterand the star formation history of the universe.

36Active star formation in the Antennae galaxies
NGC 4038
NGC 4038

NGC 4039r- Many SSCs are located inthe overlap region( 40% of youngest star clusters arelocated; Wilson et al. 2003)- 5 out of 8 young massive cluster(106 M > M , age <10 Myr )exist in the overlap region

NGC 4039

Gilbert & Graham 2007;
Whitmore et al. 2010

37

''

0th moment [K km/s]
12CO (3-2) Tsuge+ 2019
Dataset: ALMA
0.00
300.00 600.00 900.00

,,D2

D,

ALMA cycle0, Band 7 (345 GHz)

D1

SGMC 1.

C

SGMC 2500 pc
SGMC B1
4/51mSGMC:
56.0s Super Giant Molecular
55.0s Complex
Right Ascension (J2000)

project

2011.0.00876

Angularresolution~ 0.”70 x 0.”46

Spatialresolution~70 × ~50 pc

Velocity
resolution

5.0 km s-1

1σ RMS
at velocity
resolution~ 4.8 × 10-3
Jy/beamreference

Whitmore et al.
2014., ,,,38

Velocity distribution
80 km s−1

SGMC 1110 km s−1

SGMC 290 km s−1

SGMC
4/539

Discussion: cloud-cloud collision toward SSC B1◼ Observational signatures of the cloud-cloud collision
Observation: Furukawa et al. 2009 ; Ohama et al. 2010 ; Fukui et al. 2014 , 2015 , 2016 , 2017 ; Torii et al. 2011 , 2015 ,2017 ;Saigo et al. 2017, etc… , Numerical calculation; Habe & Ohta 1992; Anathpindika 2010; Takahira et al. 2014

Complementary distribution

Bridgefeatures

Bridgefeatures

40

Discussion: Time scale of collision
Relative motion of two velocity components haveinclination angle to the line of sight
After collision41

Discussion: Time scale of collision
Relative motion of two velocity components have
inclination angle to the line of sight
Displaced

During collision

42

Discussion: Time scale of collision
The two velocity components with displacement of ~ 92 pc
Collision timescale: ~1 Myr
105 pc / 113 km s-1 = 0.9 Myr
The angle of the relative motion tothe line of sight is assumed to be 45 Cluster age: ~ 1 Myr(Whitmore et al. 2010)

Collision time scale isroughly consistent with thecluster age.

43

Spatial resolution is insufficient
Cycle0

数値計算
simulation~100 pc scale Numerical(0.50.7 “)contour: Blue-shifted cloud
image: Red-shifted cloud

B1

Takahira et al. 2014

-High resolution better than 15 pc will be required (size of SSC <15 pc)
Detailed complementary spatial distribution suggested bynumerical simulation cannot be verified.
=> Uncertainty of estimation of the displacement distance and angle is large. 44A5@• ,-"=D89O 24FE3;2
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