Forma<on of Filamentary HI/Molecular
Clouds and Role of Magne<c Fields

Tsuyoshi Inoue
Department of Physics, Nagoya Univ.
Inoue & Inutsuka 2016, ApJ, 833, 10Inoue, Hennebelle, Fukui, Matsumoto, Iwasaki & Inutsuka 2018, PASJ accepted.

Outlinep Forma<on of ﬁlamentary HI clouds (HI ﬁbers) our of shocked diﬀuse ISM(Inoue & Inutsuka 08, 09, 16)

p Forma<on of star forming ﬁlaments our of shocked molecular gas clumps(Inoue+18)

HI Fibers
p The Galac<c Arecibo L-Band Feed Array HI (GALFA-HI) Survey.

NHIB orienta<on from starlight pol.

Filamentary HI clouds iden<ﬁed by the RHT method (Clark+14, 15)

p Angular correla<on between ﬁbers and B-ﬁeld (Clark+14)
l Good correla<on with Plank Polariza<on data.
(Clark+15)
l B-ﬁeld orienta<on is measured only
from gas structures!?
p These HI ﬁbers are embedded in shell of Local bubble （see also McClure-Griﬃths+ 06）.

The Rolling Hough Transformp A machine vision transforma<on technique to extract linear structures （Clark+14）
Original image

Smoothed image using
top-hat kernel of diameter DK

DK

Subtrac<on

DW

Pudng rolling slit of size DW to ﬁnd linear
structures of length larger than DW.
Angle to local B ﬁeld is measured when
the linear structure is detected.

l DK ~ 0.1 pc, DW ~ 1 pc is appliedà Linear structures of width <~ 0.1 pc andlength ~> 1 pc are extracted.

Impact of Magne<c Field

cooling

p Evolu<onally track is dras<cally changed due to the eﬀect of magne<c pressure.
(Inoue & Inutsuka 08, 09)

熱不安定

l Many observed characteris<cs of HI clouds（Heiles & Troland 03） are reproduced.
i) morphology (raspect~50), ii) strength of B(β < 1), iii) moderate turbulence(M~2)

3D MHD Simula<on of HI Cloud Forma<on
Inoue & Inutsuka 16, ApJ
p We have updated simula<ons to 3D to study morphological proper<es of HI clouds.

Model Parameters
Ini<al level ofIni<al B angle
turbulencev = 15 km/s

B0Θ

Fibers Iden<ﬁed by RHT
p W/O ini<al turbulence, orienta<on of ﬁbers tend to be parallel to B-ﬁeld for low Θ,
while it becomes perpendicular for large Θ.
B0B0

Angular PDF of Fiber Orienta<on
Inoue & Inutsuka 16, ApJ

Fibers Iden<ﬁed by RHT
p With ini<al turbulence, orienta<on of ﬁbers is parallel to B-ﬁeld independent of Θ,
though dispersion is large.

Angular PDF of Fiber Orienta<on
p With ini<al turbulence, orienta<on of ﬁbers is parallel to B-ﬁeld independent of Θ,
though dispersion is large.
Inoue & Inutsuka 16, ApJl Angular dispersion ~ 40° is consistent with Planck observa<on (Solar+16).

Why？

Inoue & Inutsuka 16, ApJp Shear of velocity along B-ﬁeld plays key role.

Bshear strength : S [ km/s/pc ]2.0v

1.51.02.11 cosΘ

0.0v: Θ22V0-Θ90V0w/o ini<al Δv
with ini<al Δv: Θ22V5-Θ90V5

0.50

102030 40 50 60 70
initial angle : Θ [ deg. ]8090l Fibers that align with B-ﬁeld is created when the shear along B-ﬁeld is larger thanthe cri<cal value of ~ 1 km/s/pc.
l W/o ini<al turbulence, it is known that velocity shear is created at shock front whosestrength is decrease with Θ (∝ cos Θ) (e.g., Inoue et al. 2013, ApJ, 772, L20）
à In realis<c ISM with turbulence, we can always expect ﬁbers along B-ﬁeld.

Strong Shock as Trigger of Massive
Star Forma<onp Recent observa<ons suggest massive star/cluster forma<on is triggered by cloud collision（e.g., Furukawa+09, Ohama+10 for Westerlund2, Torii+11, 15 for M20 & RCW120,Fukui+14 for NGC3603, Nakamura+14 for Serpens South）.

l Representa<ve sites of cloud-cloud
collision where massive stars arelocated at center of each panels.
l Large collision velocity for
massive star forma<on:ü vrel ~ 20 km/s>> cs ~ 0.2 km/s
à Strong shock triggers
massive star forma<on?
Color: Spitzer 8, 24µm (Benjamin+03, Carey+09)
Contour: NANTEN2 12CO J=1-0 (Fukui+)Filaments
p Recent observa<ons established that dense ﬁlament is the terminal of ISM evolu<on.
l Low mass stars are formed from ﬁlament with mline>mcrit for GI (Andre+10).
l Global collapse of massive ﬁlament drives massive-star forma<on (Prepo+13).
Spitzer 8µm+N2H+ (1-0) by IRAM30mHerschel Aquilaﬁlaments

SDC13

p Cloud collision と フィラメントからの大質量形成がつながると面白い。

Shock Crushing of Turbulent Cloud
Inoue & Fukui 13, Inoue+18 PASJ special issue
p AMR MHD simula<on of cloud collision by SFUMATO code (Matsumoto 07).
l Collision of a turbulent cloud and a bigger cloud with eﬀec<ve resolu<on 40963 cells (Δx~0.0015 pc).
l M = 500 msun, δv=1.5 km/s for small cloud.
l 〈n〉=1000 cm-3, By=10 µG, vrel=10 km/s.

Filament Forma<on by Clump CrushingInoue & Fukui 13, Inoue+17 in prep.
p Filaments are formed even if self-gravity is switched oﬀ.
with self-Gravity

B0

w/o self-Gravity

B0

p Filaments are formed by magneto-hydrodynamic process.

Filament Forma<on behind MHD ShockInoue & Fukui 13, Vaidya+13
p What happens when a dense clump is swept by a shock?

1shockshock2

dense clump

3shockv
yyz

x

Bzyv
x

Bz

x

oblique shockv＊ a ﬁlament perpendicular to the screen is formed by this process.

BFocused Flow by Oblique ShockInoue+18
1000 μG
column density : Log [ NH2 (cm -2) ]5.0 km/s

実際のシミュレーションデータでも Inoue & Fukui (2013) 機構を確認

Massive Star Forma<onInoue+18
p Collapse of massive ﬁlament leads forma<on of massive core (sink).

with self-Gravity

Log ( NH2 [cm-2] )duration = 0.7 Myrl Up to n ~ 8 × 106 cm-3, thermal Jeans
length is resolved more than 8 cells(the Jeans criterion; Truelove+97).
l Above n ~ 8 × 106 cm-3, sink par<cle isintroduced if the region shows signaturesof gravita<onal collapse (div. v <0, Etot<0,Eigenvalue of grd. v tensor < 0).

B0l The most massive sink mass ~ 50 msun

Accre<on Rate
Mass of sink [ msun ]accretion rate [ msun/yr ]p The most massive sink grow with high accre<on rate

Inoue+17 in prep.

.

l Most massive sink grow with constant, high, accre<on rate: Macc > 10-4 msun/yr.
l High accre<on rate is kept for a long <me so long as the ﬁlament collapse con<nues.

Role of B Fieldp Cri<cal line-mass for ﬁlament with perp. B ﬁeld (Tomisaka 14).

Bw

where Φ = B w.
~ 15 Ms/pcB ﬁeld contribu<on dominate, if B > 35 µG (cs/0.2 km/s)2 (w/0.1pc)-1.
p Typical B ﬁeld in the shock induced ﬁlament (Inoue & Fukui 13):

vshBfilament ≈ 2Bini = 8π ρini v sh ~ 300 µG (nini/103 cm-3)1/2 (vsh/10 km/s).
vAlf
à The cri<cal line-mass of the shock induced ﬁlament can be much larger than
the thermally supported ﬁlament.

Colmn density map

Vz [km/s]
Posi<on along red line

p P-V map of a ﬁlament formed inInoue+18 paper.

Posi<on along blue lineP-V Structure of Simulated FilamentVz [km/s]

Summaryp Correla<on between HI ﬁlament (ﬁber) orienta<on and B-ﬁeld is studied.
(Inoue & Inutsuka 16)l Good correla<on HI ﬁbers and B ﬁeld is due to turbulent stretching.
l Turbulence does not give perfect alignment, but there is always small misalignment.
ü Applica<on to the Chandrasekhar-Fermi method is not recommended.
p Forma<on of (massive) molecular ﬁlaments by shock compression are studied.
(Inoue+18)
l Filaments are formed by Inoue & Fukui 12 mechanism.
l Filament line-mass seems to be determined by B-ﬁeld es<mated from Tomisaka formula.
l Posi<on-Velocity structure of ﬁlament forma<on cite shows nice similarity to observed
young ﬁlament (Arzoumanian+ in progress).