Galactic - Center Arc & Threads: Current sheet model Y. - - PowerPoint PPT Presentation

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Galactic - Center Arc & Threads: Current sheet model Y. - - PowerPoint PPT Presentation

Oct 08, 2022 117 likes •483 views

Galactic - Center Arc & Threads: Current sheet model Y. Sofue, H. Kigure & K. Shibata 2005 Nov 17-18 @ MHD WS, Chiba University Radio 10 GHz (3cm) Radio 10 GHz (3cm) 6x3 deg, Nobeyama 6x3 deg, Nobeyama 45m 45m Sofue Sofue

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Galactic -Center Arc & Threads:

Current sheet model

  • Y. Sofue, H. Kigure & K. Shibata

2005 Nov 17-18 @ MHD WS, Chiba University

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Radio 10 GHz (3cm)

Radio 10 GHz (3cm) 6x3 deg, Nobeyama

6x3 deg, Nobeyama 45m 45m

Sofue

Sofue et al. 1985 t al. 1985

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Vertical Magnetic Field in GC

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Radio 1.4 GHz (VLA Y

Radio 1.4 GHz (VLA Yusef-Zadeh,Morris sef-Zadeh,Morris)

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Radio 5 GHz (VLA Yusef-Zadeh,Morris)

Radio 5 GHz (VLA Yusef-Zadeh,Morris)

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Radio Threads

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SLIDE 7

Radio 90 cm (VLA RaLosa

Radio 90 cm (VLA RaLosa et al.) t al.)

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SLIDE 8

90 cm

(Anantharamaiah

et al. 1991)

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Past models for the radio arc

Sofue, Fujimoto 1987; Benford 1988 : B⊥ x Bφ (V) Dahlburg et al. 2002: B x Cloud instability

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Interaction of Verticld Magnetic field and Rotating Gas

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5 cm polarization (Sofue et al.)

RM>0 RM<0

3 cm polarization (Tsuboi et al.)

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Tw isted vertical magnetic field in GC

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Origin of Vertical Origin of Vertical field in GC field in GC

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High-velocity rotation and dispersion of Molecular Clouds

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Molecular ring/clouds in GC Molecular ring/clouds in GC

(CO Line BTL 7m Bally et al. ) (CO Line BTL 7m Bally et al. )

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Face-on View Face-on View

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3 2 1 0 -1 deg 300

200 100

  • 100
  • 200
  • 300

V km/s Long CO line LV Diagram High-velocity Rotation & Dispersion

  • f Gas
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Magnetic reconnection and Current Sheet model

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Thread properties Local, Isolated Thin/narrow Non-axisymmetric No energy injection (such as jets) High contrast against backgr.

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GC MHD circumstance Vertical magnetic field Molecular clouds High-rotation (deep grav.pot) High-velocity dispersion

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Origin of Threads

BH

Cloud Accretion

B

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Accretion + Amplification

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Winding, Tw isting

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Winding, Tw isting, Kinking

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  • Reconnection
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Thread

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Threads

Intermittent accretion

  • f Clouds
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MHD Simulation of Threads and Arc Non-axisymmetric 3D

(Method: Kigure et al. 2005)

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171x100x480 r,phi,z meshes

Current B + Cloud

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90 cm (LaRosa et al. 2000)

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High contrast of radio brightness

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Flux of released energy along the

current sheet (thread) by Bz x Bφ term = Poyinting flux

f = BzBφV/4π

thread

f0= Bz0Bφ0V0/4π ambient

Ratio of tread/ambient fluxes

r = f/f0 = Bφ/Bφ０V/V0 >>1

because Bφ０～ 0

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SLIDE 34

Radio brightness Σ= 2k Tb/λ2 = δf/ν ~ δ (Bφ/B0)B02 V / 4πν

δ=Efficiency of Poynting flux to Radio flux (CR

  • accel. Etc)

ν～1 GHz V ~ 100 km/s, B0 ~ 100 μG From simulation Bφ/B0 ~ 0.1 . Hence, Tb ~ 10 -4 δ K. Observation: Tb ~ 0.1 – 1 K δ ~ 10 -4 -10 -5

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Thread properties understood by Current sheet model: Local, Isolated, narrow Non-axisymmetric No energy injection High contrast against backgr.

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