Dec.22, 2017 @Kagoshima Univ.

Kensuke Kakiuchi (Nagoya Univ./ The Univ. of Tokyo)
Collaborators:
Takeru K. Suzuki (The Univ. of Tokyo/ Nagoya Univ.),
Yasuo Fukui(Nagoya Univ.), Kazufumi Torii(NRO),
Mami Machida(Kyusyu Univ.), Ryoji Matsumoto (Chiba Univ.)
Kakiuchi et al. In prep. (ArXiv:1712.04209)

Outline The Galactic Center (GC) region

300

10020010100

01-100-200

0.1-300
420 -2-4

Galactic longitude (degree)

Column density (1021 cm-2)

 Rising loops andfast downflows

Simulated l-v diagram

LoS velocity (km s-1)

 Vertical structure
in MHD simulation data

The galactic center (GC) region: Within a few parsec region
200pc

8.0kpc銀河面
Galacticplane

Sgr AThe Sun

Radio continuum (330MHz; LaRosa et al. 2000)✓ Super massive BH Sgr A*, massive star cluster, SNR✓ 5-10 % of total molecular gas in the Milky Way collected.
✓ Molecular gas: High density, High temperature

Velocity structure in the GC region

1010
987655
432
100

250

100
0-100-200200
200

Radial distance at center

200

150

100
100

5000-50-100-100-150-200-200-250

5500-5-5Longitude

Galactic longitude[degree]
50-5

Galactic longitude [degree]

Complex structure

Distance from GC (kpc)

Only circular motion
Line of sight velocity

300

Color : column density
N(H2)/I(CO) ≒ 2.3 x 1020cm-2(K km s-1)-1)

LOS vel. [km/s]

Line of sight velocity [km/s]- 12CO(1-0) map NANTEN (Torii+10) -Non-circular motion

Bar potential → Non-circular motion ?
❖ Orbital calculation (Binney+1991)

0-0.5B

A-0.2 0 0.2

X [kpc]

200

AB

100
0-100-2004 2 0 -2 -4 4 2 0 -2 -4Galactic longitude [deg]Line of sight velocity [km/s]

Y [kpc]0.5LoS velocity [km s-1]

- Bar-like stellar gravitational potential (detected near 3kpc)→ gas motion in the GC region ?
- As a result, the gas is excited radial motion on bar potential- However, complex features cannot is reproduced, even if 3D
simulation (Rodriguez-Fernandez & Combes 2008).
300
200
1000-100-200
50-5Galactic longitude [degree]Bar potential v.s. Magnetic Field !
❖ Polarization observation(Chuss+2003, Nishiyama+ 2010)✓ Detection of vertical field and pallarel field(Disccusion: non-thermal filament structure)❖ Large magnetic field strength(※typical strength is 1μG @ molecular cloud in disk region)✓ globally > 50μG (Crocker + 2010)✓ Locally ~ 0.1-1mG (Yuzef-Zadeh+1984)✓ Inner the dark cloud 2-5 mG (Pilai et al. 2015)❖ The loop structure of molecular cloud(Fukui+06, Machida+09, Torii+10a,b)✓ It has potential that it is sign of Parker Instability.

Vertical Structure

12CO(1-0) mapNANTEN (Torii+10)

4Galactic latitude

20-2-450-5

Galactic longitude- Vertical motion can play important rolesc.f. The Galactic center radio lobe (GCL; Sofue & Handa 1984)
Double helix structure (Enokiya+2014)

Parker Instability

Parker (1966,1967),
Matsumoto et al.(1988)

Magnetic buoyancy > Gravity force
Vertical component of magnetic field :Fluid particle
Low

Magneticbuoyancy

Gas flow

HighGravity

PB ∝ B2: unstable: stable

Gravitational energy→ kinematic energy

MHD simulation in the GC region(Suzuki+2015, cf, Machida+2009)❖ SETUP✓ Axismetry gravitational potential(Miyamoto & Nagai 1975)

Initial magnetic field:

LoS velocity (km s-1)

✓ Ideal MHD & locally isothermal gas

300

1002001010001-100-200

0.1-300
4

Initial gas profile: hydrostatic equilibrium

20 -2-4

Galactic longitude (degree)

Column density (1021 cm-2)

Simulated l-v diagram

Non-circular motion : excited by magnetic activity
Observational features(e.g. parallelogram structure) reproduce

Overview: Radius vs velocity(Averaged 0<φ<2π, |z| < 1 kpc)

Initial rotational speed:~ 50-200 km/s

RMS (root mean square)Vertical speed:~ 10-30 km/s

Vertical motion excited by magnetic activity

Overview: Mass flux to vertical direction~ upflow speed

Free fall velocity ~ downflow speedOverview: Gas flows and structure in global--track the motions of fulid elements with t=399.5-402.5Myr.

✓ Ubiquitously, vertical flows exist

Average life ~ 4-6 Myr

Overview: Gas flows and structure in global--track the motions of fulid elements with t=399.5-402.5Myr.

Overview: Gas flows and structure in global--track the motions of fulid elements with t=399.5-402.5Myr.
~ upflow speed

Free fall velocity ~ downflow speedOverview: Gas flows and structure in global--track the motions of fulid elements with t=399.5-402.5Myr.

Region X

Overview: Gas flows and structure in global--track the motions of fulid elements with t=399.5-402.5Myr.

Region XObserver

Simulated l-v diagram
High LoS velocity(t＝401.0 Myr)LoS velocity (km s-1)

200
1010001-100-2000.1-300
420-2

Column density (1021 cm-2)

100300y90135451800225

315
270x-4Galactic longitude (degree)

視点(270°)(r=8.0kpc)

Simulated l-v diagram(t＝401.0 Myr)High LoS velocity

LoS velocity (km s-1)

Column density (1021 cm-2)

100300Large
velocity dispersion
10200
10001-100-200

0.1-300
420-2y90
13545

1800225315
270x-4Galactic longitude (degree)

Obs.(270°)(r=8.0kpc)

Magnetic field line in region X
Region XZ (kpc)

MF1zoomZ (kpc)

MF2✓ Magnetic arch-like structure !

Distance along Magnetic Fieldline (kpc)

Rising loop & Fast downflows
MF1

Z (kpc)Z (kpc)Velocity (km/s)

Velocity (km/s)

MF2

Distance along Magnetic Fieldline (kpc)

Distance along Magnetic Fieldline (kpc)✓ Loop-foot (A): downflows ~100 km/s

The gases fall down to one side

✓ Loop-top (B): Rising ~ 50 km/s

Vertical velocity ↑Rising loop & Fast downflows
MF1

Z (kpc)Z (kpc)Number density (cm-3)

Number density (cm-3)

MF2

Distance along Magnetic Fieldline (kpc)

Distance along Magnetic Fieldline (kpc)✓ Downflows with high density✓ The gases collect and compress

Rising loop & Fast downflows
MF1Z (kpc)

Z (kpc)Number density (cm-3)

Number density (cm-3)

MF2

Distance along Magnetic Fieldline (kpc)

Distance along Magnetic Fieldline (kpc)✓ Downflows with high density✓ The gases collect and compress

Discussion – Region X in l-v diagram✓ Different features depending on the viewing angle.

LoS velocity (km s-1)

100

300
200

10

100
01-100-200

0.1

-300
420-2-4420-2-4

Column density (1021 cm-2)

Obs.3 (250°)

Obs.2 (210°)y・Velocity dispersion

451800225

315270Galactic longitude (degree)・Shape90135xObs.2 (210°)(r=8.0kpc)
Obs.3 (250°)(r=8.0kpc)

Summary
100

LoS velocity (km s-1)

300

Column density (1021 cm-2)

High velocity
Largevelocity dispersion
10200
10001-100-200

Gas flows

compression

Magnetic buoyancy
Gravity

0.1-300
420-2-4

Galactic longitude (degree)

High velocity(Magnetic Activity; Parker Instability)

Downflows along the line of sightLarge velocity dispersion

Fall down align the magnetic slope Acceleration : ~100 km/s
Footpointcollect
42of slope:
0-2-4 and compress gases

Appendix: Basic Equation
Eq. of continuity

Eq. of motion

Eq. of Induction

Axisymmetry gravitational potential(Miyamoto & Nagai 1975)

Magnetic Field in The Galactic Centre Region❖ Strong magnetic fields✓ globally > 50μG (Crocker+ 2010)✓ Locally ~ 100-1000μG (Yuzef-Zadeh+ 1984; Morris 1990; Pillai+15)(※ a few μG in a typical molecular cloud at the disk)❖ Amplification of Magnetic fields

MRIParker Instability

Differential rotation