DYNAMO ACTIVITIES DRIVEN BY MAGNETOROTATIONAL INSTABILITY AND THE PARKER INSTABILITY IN GALACTIC GASEOUS DISKS

Journal Article · Sun Feb 10 04:00:00 EST 2013 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/764/1/81· OSTI ID:22167773

Machida, Mami ^[1]; Nakamura, Kenji E. ^[2]; Kudoh, Takahiro ^[3]; Akahori, Takuya ^[4]; Sofue, Yoshiaki ^[5]; Matsumoto, Ryoji ^[6]

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1. Department of Physics, Faculty of Sciences, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581 (Japan)
2. Department of Mechanical Engineering, Kyushu Sangyo University, 2-3-1 Matsukadai, Higashi-ku, Fukuoka 813-8503 (Japan)
3. National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588 (Japan)
4. Korea Astronomy and Space Science Institute, Daedeokdaero 776, Yuseong-Gu, Daejeon 305-348 (Korea, Republic of)
5. Institute of Astronomy, University of Tokyo, Mitaka 181-8588, Tokyo (Japan)
6. Department of Physics, Graduate School of Science, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522 (Japan)

We carried out global three-dimensional magnetohydrodynamic simulations of dynamo activities in galactic gaseous disks without assuming equatorial symmetry. Numerical results indicate the growth of azimuthal magnetic fields non-symmetric to the equatorial plane. As the magnetorotational instability (MRI) grows, the mean strength of magnetic fields is amplified until the magnetic pressure becomes as large as 10% of the gas pressure. When the local plasma {beta} (=p {sub gas}/p {sub mag}) becomes less than 5 near the disk surface, magnetic flux escapes from the disk by the Parker instability within one rotation period of the disk. The buoyant escape of coherent magnetic fields drives dynamo activities by generating disk magnetic fields with opposite polarity to satisfy the magnetic flux conservation. The flotation of the azimuthal magnetic flux from the disk and the subsequent amplification of disk magnetic field by the MRI drive quasi-periodic reversal of azimuthal magnetic fields on a timescale of 10 rotation periods. Since the rotation speed decreases with radius, the interval between the reversal of azimuthal magnetic fields increases with radius. The rotation measure computed from the numerical results shows symmetry corresponding to a dipole field.

• OSTI ID: 22167773
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 764; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
FLOTATION
GALAXIES
INSTABILITY
MAGNETIC DISKS
MAGNETIC FIELDS
MAGNETIC FLUX
MAGNETOHYDRODYNAMICS
PERIODICITY
PLASMA
ROTATION
SIMULATION
SYMMETRY
THREE-DIMENSIONAL CALCULATIONS