Radio broad-band visualization of global three-dimensional magnetohydrodynamical simulations of spiral galaxies - II. Faraday depolarization from 100 MHz to 10 GHz

M. Machida, T. Akahori, K. E. Nakamura, H. Nakanishi, M. Haverkorn

研究成果: ジャーナルへの寄稿記事

1 引用 (Scopus)

抄録

Observational study of galactic magnetic fields is limited by projected observables. Comparison with numerical simulations is helpful to understand the real structures, and observational visualization of numerical data is an important task.Machida et al. (2018) have reported Faraday depth maps obtained from numerical simulations. They showed that the relation between azimuthal angle and Faraday depth depends on the inclination angle. In this paper, we investigate 100MHz to 10 GHz radio synchrotron emission from spiral galaxies, using the data of global three-dimensional magnetohydrodynamic simulations. We model internal and external Faraday depolarization at small scales and assume a frequency-independent depolarization. It is found that the internal and external Faraday depolarization becomes comparable inside the disc and the dispersion of Faraday depth becomes about 4 radm-2 for face-on view and 40 radm-2 for edge-on view, respectively. The internal depolarization becomes ineffective in the halo. Because of the magnetic turbulence inside the disc, frequency-independent depolarization works well and the polarization degree becomes 0.3 at high frequency. When the observed frequency is in the 100 MHz band, polarized intensity vanishes in the disc, while that from the halo can be observed. Because the remaining component of polarized intensity is weak in the halo and the polarization degree is about a few per cent, it may be difficult to observe that component. These results indicate that the structures of global magnetic fields in spiral galaxies could be elucidated, if broad-band polarimetry such as that with the Square Kilometre Array is achieved.

元の言語英語
ページ(範囲)3394-3402
ページ数9
ジャーナルMonthly Notices of the Royal Astronomical Society
482
発行部数3
DOI
出版物ステータス出版済み - 1 1 2019

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spiral galaxies
depolarization
visualization
radio
broadband
polarization
halos
magnetic field
simulation
magnetohydrodynamics
interstellar magnetic fields
turbulence
magnetohydrodynamic simulation
polarimetry
inclination
synchrotrons
magnetic fields

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

これを引用

Radio broad-band visualization of global three-dimensional magnetohydrodynamical simulations of spiral galaxies - II. Faraday depolarization from 100 MHz to 10 GHz. / Machida, M.; Akahori, T.; Nakamura, K. E.; Nakanishi, H.; Haverkorn, M.

:: Monthly Notices of the Royal Astronomical Society, 巻 482, 番号 3, 01.01.2019, p. 3394-3402.

研究成果: ジャーナルへの寄稿記事

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abstract = "Observational study of galactic magnetic fields is limited by projected observables. Comparison with numerical simulations is helpful to understand the real structures, and observational visualization of numerical data is an important task.Machida et al. (2018) have reported Faraday depth maps obtained from numerical simulations. They showed that the relation between azimuthal angle and Faraday depth depends on the inclination angle. In this paper, we investigate 100MHz to 10 GHz radio synchrotron emission from spiral galaxies, using the data of global three-dimensional magnetohydrodynamic simulations. We model internal and external Faraday depolarization at small scales and assume a frequency-independent depolarization. It is found that the internal and external Faraday depolarization becomes comparable inside the disc and the dispersion of Faraday depth becomes about 4 radm-2 for face-on view and 40 radm-2 for edge-on view, respectively. The internal depolarization becomes ineffective in the halo. Because of the magnetic turbulence inside the disc, frequency-independent depolarization works well and the polarization degree becomes 0.3 at high frequency. When the observed frequency is in the 100 MHz band, polarized intensity vanishes in the disc, while that from the halo can be observed. Because the remaining component of polarized intensity is weak in the halo and the polarization degree is about a few per cent, it may be difficult to observe that component. These results indicate that the structures of global magnetic fields in spiral galaxies could be elucidated, if broad-band polarimetry such as that with the Square Kilometre Array is achieved.",
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