Triggered massive starformation induced by galaxy
interaction and cloud collision
Kengo Tachihara, Kisetsu Tsuge, Yasuo Fukui(Nagoya University)

Super-star cluster RMC 136 (R136)

R144 binary- Yung cluster : ~ 1.5 Myr- The most massive in the local group: ~105 M☉- Super-massive stars
265 M☉, 195 M☉, 175 M☉, 135 M☉ (Crowther et al. 2010)

The most massive stars and binaries• The most massive star R136a1 (SpT=WN5h): 265 M atpresent and 320 M at birth• The most massive binary R144 (SpT=WN6h): total 200-300 M
at present, 400 M at birth• Both are in 30 Dor in the LMC• in R136 10 stars with M > 50 M
• Galactic analog: NGC3603-A1 eclipsing binary (116+86 M )• They are all Black Hole progenitors• Period of R144 1 year => orbital semi-major axis
• Black hole binary progenitor

10 AU

Formation of (Galactic) super-star clusters• Westerlund 2 cloud• Clusters of ~300 YSOs,5000 Mo•• 2 molecular clouds withMcloud ~ 105 Mo

different V by ~ 16 km/s

• Triggered formation byCloud-cloud collision(Furukawa+ 2009; Ohama+ 2010)

Super-star cluster
R136The Large Magellanic Cloud (LMC)
distance : ~ 50 kpc
Inclination : ~ 30 deg.

5

Atomic gas HI 21 cm
Molecular gas 12CO (J = 1-0)
2 velocity components separated by ~ 50 km/s
L-component(Low velocity)

D-component(Disk)

R136

+200

250
Vlsr [km/s]

300Separation of L- & D-components

P-V diagram

The bridge feature connecting
the 2 velocity components

image: HI, contour: COComplementary distribution of the 2 components

complementary distribution with displacement ~ 200 to 300 pc
Collision time scale ~ 2.4 to 3.6 Myr

HI intensity [K km/s]

Variation in gas/dust ratio

Planck dust
opacity map

Dust optical depth (𝜏353)

Large gas/dust ration in the region with the L-component=> possible contamination of low-metal gas from the SMC

The Magellanic bridge (LMC - SMC tidal interaction)
The HI Parkes All-Sky Survey (HIPASS)
ave. beam size: 15.5 arcmin.

SMCNGC
602+
LMC

Magellanicbridge+ R136
Putman et al. (1998)
Image: HI 21 cm

The Small Magellanic Cloud: SMC
NGC 602 in N90

N71

N80

N76
N66

N50
N36
N84
N90

NGC 346 in N66

Atomic hydrogen HI
21 cm line(L. Staveley-Smith et al. 1997)

Molecular cloud
12CO(J = 1-0)
(NANTEN)
The HI 21 cm line
typical spectrum

Scatter plot between τ353 and W(HI)
L-component

NGC602

D-component

NGC602

Extended L-component distribution

The Small Magellanic Cloud (SMC): NGC 602

15

The Small Magellanic Cloud (SMC): NGC 602

Collision timescale ~ 300 pc / 40 km s−1 ~ 8 Myr

The Small Magellanic Cloud (SMC): NGC 602
Dec.-velocity diagram
LD17

Mixture of the gas

Gas/dust ratio variation

M33 and a supermassive cluster NGC 604
The M31-M33 streamM3165 kpc

M33NGC 604 by
HST WFPC

M33 spiral galaxy at 794 kpc
a member of the local group

2nd largest HII region in the local group~ 200 OB stars
360 pc x 450 pc in size
~ 3 Myr oldin analogous to R136 in LMC(Tachihara et al. 2018)

Numerical simulation of colliding gas ﬂow
10 km s−1

1.5

5.0z

1.0
4.0

3.5
0.5
3.5

yx

0.0
−1.5

Simulation by Inoue & Fukui (2013)

1 pczyx

Cores identiﬁed by CLUMPFINDx (pc)

−0.5

3.00.010 km s−1

1.2(b)y (pc)

(a)

−1.0

log [mean nH2 (cm−3)]

4.0

4.5

y (pc)

4.5log(n [cm−3])

5.0

1.1

1.0
−1.0

−0.9

−0.8

−0.7−0.6

x (pc)

V-ﬁeld(Fukui et al. 2019 submitted)

Filaments and cores
(2)

(1)

103
102
101(2)

103
102
10114
yH2 column density (1022 cm−2)12(3)1 pc(4)
Nmassive core = 5108(3)

Nmassive core = 7 103
102
101(4)

Nmassive core = 4 103
102
101(5)

103
102
101(8)

Nmassive core = 1 103
102
101212223101010
NH2 (cm−2)

(5)

64(6)

2

Nmassive core = 9(6)

1020

1021

1022
1023
NH2 (cm−2)

(8)

(7)

(7)

1020

1021

1022
1023
NH2 (cm−2)

1020

Number of pixelszNumber of pixels(1)

Number of pixels

toward massive cores (×10)

Histogramsof column density
3is excluded) in the y-z plane at t = 0.7 Myr (top-left panel) and column density

Fig. 11. Column density map of H2 (low density gas with < 104 cm

histogram in the 8 regions of 1.5 pc ⇥ 1.5 pc (panels (1) – (8)). The crosses in the top-left panel show the positions of massive cores with M> 10 M

Identiﬁed dense coresCore Mass Function
103
Mcore > Mj

W43 cores(Motte et al. 2018)102

RCW38 cores(Torii et al. 2019)6b/cdN / dlog(Mcore / M⊙)

Mcore > Mjeff

4mean(a / b) = 1.9 ± 0.88Mcore > 10 M⊙ and Mcore > Mjeff

Axial ratiomean(b / c) = 2.5 ± 0.9
10Kroupa (2001) IMF

2Chabrier (2005) IMF

110−2

10−1

1

Mcore (M⊙)

10102002

4a/b6

Massive cores are tend tobe in oblate shape8

Angular momentum of the massive cores
L vs major-axis

L vs 2nd-major-axis

Massive cores tend to be oblate,and spinning around the minor axis
formation of massive binaries(?)

L vs minor-axis

L vs B

Conclusion• Super star clusters and very massive stars are likely to formby cloud-cloud collision• Galaxy interaction induces HI gas collision• Tidal interaction between the Magellanic clouds induced thecloud collision via HI gas exchange• Numerical simulation successfully reproduce dense coresfrom ﬁlaments• Collision of high column density clouds is preferable formassive cluster formation• The simulated massive cores tend to be in oblate shapespinning around the minor axis, and may evolve into BH
binaries