Kensuke Kakiuchi (Nagoya Univ./ The Univ. of Tokyo)

Transcription

1 Dec.22, 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: )

2 LoS velocity (km s -1 ) Column density (1 21 cm -2 ) Outline The Galactic Center (GC) region Vertical structure in MHD simulation data Rising loops and fast downflows Simulated l-v diagram Galactic longitude (degree)

3 The galactic center (GC) region : Within a few parsec region 2pc 8.kpc Galactic 銀河面 plane Sgr A The Sun Radio continuum (33MHz; LaRosa et al. 2) Super massive BH Sgr A*, massive star cluster, SNR 5-1 % of total molecular gas in the Milky Way collected. Molecular gas: High density, High temperature

4 Line of sight velocity [km/s] LOS vel. [km/s] Line of sight velocity Radial distance at center Distance from GC (kpc) Velocity structure in the GC region - 12 CO(1-) map NANTEN (Torii+1) - Color : column density N(H2)/I(CO) 2.3 x 1 2 cm -2 (K km s -1 ) -1 ) 5-5 Galactic longitude [degree] Only circular motion Longitude Galactic longitude[degree] Complex structure Non-circular motion

5 Line of sight velocity [km/s] Bar potential Non-circular motion? Orbital calculation (Binney+1991) - 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 28). Y [kpc] A.2 X [kpc] B LoS velocity [km s -1 ] A Galactic longitude [deg] 4 B Galactic longitude [degree]

6 Bar potential v.s. Magnetic Field! Polarization observation (Chuss+23, Nishiyama+ 21) Detection of vertical field and pallarel field (Disccusion: non-thermal filament structure) Large magnetic field strength ( typical strength is molecular cloud in disk region) globally > 5μG (Crocker + 21) Locally ~.1-1mG (Yuzef-Zadeh+1984) Inner the dark cloud 2-5 mg (Pilai et al. 215) The loop structure of molecular cloud (Fukui+6, Machida+9, Torii+1a,b) It has potential that it is sign of Parker Instability.

7 Vertical Structure 12 CO(1-) map NANTEN (Torii+1) 4 Galactic latitude Galactic longitude - Vertical motion can play important roles c.f. The Galactic center radio lobe (GCL; Sofue & Handa 1984) Double helix structure (Enokiya+214)

8 Parker Instability Magnetic buoyancy > Gravity force Vertical component of magnetic field : Parker (1966,1967), Matsumoto et al.(1988) Fluid particle Gravity Low High P B B 2 Magnetic buoyancy Gas flow : unstable : stable Gravitational energy kinematic energy

9 LoS velocity (km s -1 ) Column density (1 21 cm -2 ) SETUP MHD simulation in the GC region (Suzuki+215, cf, Machida+29) Ideal MHD & locally isothermal gas Axismetry gravitational potential Initial magnetic field: (Miyamoto & Nagai 1975) Initial gas profile: hydrostatic equilibrium Galactic longitude (degree) Non-circular motion : excited by magnetic activity Observational features(e.g. parallelogram structure) reproduce Simulated l-v diagram

10 Overview: Radius vs velocity Initial rotational speed: ~ 5-2 km/s (Averaged <φ<2π, z < 1 kpc) RMS (root mean square)vertical speed: ~ 1-3 km/s Vertical motion excited by magnetic activity

11 Overview: Mass flux to vertical direction ~ upflow speed Free fall velocity ~ downflow speed

12 Overview: Gas flows and structure in global --track the motions of fulid elements with t= myr. Ubiquitously, vertical flows exist Average life ~ 4-6 Myr

13 Overview: Gas flows and structure in global --track the motions of fulid elements with t= myr.

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

15 Overview: Gas flows and structure in global --track the motions of fulid elements with t= myr. Region X

16 Overview: Gas flows and structure in global --track the motions of fulid elements with t= myr. Region X Observer

17 Simulated l-v diagram High LoS velocity (t 41. Myr) LoS velocity (km s-1) Column density (121 cm-2) 1 3 y x -4 Galactic longitude (degree) 視点(27 ) (r=8.kpc)

18 Simulated l-v diagram (t 41. Myr) High LoS velocity LoS velocity (km s-1) Column density (121 cm-2) 1 3 Large velocity dispersion y x -4 Galactic longitude (degree) Obs.(27 ) (r=8.kpc)

19 Magnetic field line in region X Region X MF1 zoom Z (kpc) Z (kpc) MF2 Magnetic arch-like structure! Distance along Magnetic Fieldline (kpc)

20 Rising loop & Fast downflows MF1 MF2 Velocity (km/s) Z (kpc) Velocity (km/s) Z (kpc) Distance along Magnetic Fieldline (kpc) Distance along Magnetic Fieldline (kpc) Loop-foot (A): downflows ~1 km/s The gases fall down to one side Loop-top (B): Rising ~ 5 km/s Vertical velocity

21 Number density (cm -3 ) Number density (cm -3 ) Z (kpc) Z (kpc) Rising loop & Fast downflows MF1 MF2 Distance along Magnetic Fieldline (kpc) Distance along Magnetic Fieldline (kpc) Downflows with high density The gases collect and compress

22 Number density (cm -3 ) Number density (cm -3 ) Z (kpc) Z (kpc) Rising loop & Fast downflows MF1 MF2 Distance along Magnetic Fieldline (kpc) Distance along Magnetic Fieldline (kpc) Downflows with high density The gases collect and compress

23 Discussion Region X in l-v diagram Different features depending on the viewing angle. LoS velocity (km s-1) Column density (121 cm-2) Obs.3 (25 ) Obs.2 (21 ) y Velocity dispersion Galactic longitude (degree) Shape x Obs.2 (21 ) (r=8.kpc) Obs.3 (25 ) (r=8.kpc)

24 Summary 1 LoS velocity (km s-1) 3 Column density (121 cm-2) High velocity Large velocity dispersion Gas flows compression Magnetic buoyancy Gravity Galactic longitude (degree) High velocity (Magnetic Activity; Parker Instability) Downflows along the line of sight Large velocity dispersion Fall down align the magnetic slope Acceleration : ~1 km/s Footpoint collect 4 2of slope: -2-4 and compress gases

25 Appendix: Basic Equation Eq. of continuity Eq. of motion Eq. of Induction Axisymmetry gravitational potential (Miyamoto & Nagai 1975)

26 Magnetic Field in The Galactic Centre Region Strong magnetic fields globally > 5μG (Crocker+ 21) Locally ~ 1-1μG (Yuzef-Zadeh+ 1984; Morris 199; Pillai+15) ( a few μg in a typical molecular cloud at the disk) Amplification of Magnetic fields MRI Parker Instability Differential rotation