Radio broadband visualization of global three-dimensional magneto-hydrodynamical simulations of spiral galaxies I. Faraday rotation at 8GHz. (arXiv:1811.02824v1 [astro-ph.GA])

Radio broadband visualization of global three-dimensional magneto-hydrodynamical simulations of spiral galaxies I. Faraday rotation at 8GHz. (arXiv:1811.02824v1 [astro-ph.GA])
<a href="http://arxiv.org/find/astro-ph/1/au:+Machida_M/0/1/0/all/0/1">Mami Machida</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Akahori_T/0/1/0/all/0/1">Takuya Akahori</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nakanishi_K/0/1/0/all/0/1">Kenji Nakamura Hiroyuki Nakanishi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Haverkorn_M/0/1/0/all/0/1">Marijke Haverkorn</a>

Observational study of galactic magnetic fields is hampered by the fact that
the observables only probe various projections of the magnetic fields.
Comparison with numerical simulations is helpful to understand the real
structures, and observational visualization of numerical data is an important
task. In this paper, we investigate 8~GHz radio synchrotron emission from
spiral galaxies, using the data of global three-dimensional
magneto-hydrodynamic simulations. We assume a frequency independent
depolarization in our observational visualization. We find that the appearance
of the global magnetic field depends on the viewing angle: a face-on view
seemingly has hybrid magnetic field types combining axisymmetric modes with
higer order modes; at a viewing angle of $sim 70degr$, the galaxy seems to
contain a ring-like magnetic field structure; while in edge-on view, only field
structure parallel to the disk can be seen. The magnetic vector seen at 8~GHz
traces the global magnetic field inside the disk. These results indicate that
the topology of global magnetic field obtained from the relation between
azimuthal angle and Faraday depth strongly depends on the viewing anglue of the
galaxy. As one of the examples, we compare our results at a viewing angle of
$25degr$ with the results of IC342. The relation between azimuthal angle and
Faraday depth of the numerical result shows a tendency similar to IC342, such
as the peak numbers of the Faraday depth.

Observational study of galactic magnetic fields is hampered by the fact that
the observables only probe various projections of the magnetic fields.
Comparison with numerical simulations is helpful to understand the real
structures, and observational visualization of numerical data is an important
task. In this paper, we investigate 8~GHz radio synchrotron emission from
spiral galaxies, using the data of global three-dimensional
magneto-hydrodynamic simulations. We assume a frequency independent
depolarization in our observational visualization. We find that the appearance
of the global magnetic field depends on the viewing angle: a face-on view
seemingly has hybrid magnetic field types combining axisymmetric modes with
higer order modes; at a viewing angle of $sim 70degr$, the galaxy seems to
contain a ring-like magnetic field structure; while in edge-on view, only field
structure parallel to the disk can be seen. The magnetic vector seen at 8~GHz
traces the global magnetic field inside the disk. These results indicate that
the topology of global magnetic field obtained from the relation between
azimuthal angle and Faraday depth strongly depends on the viewing anglue of the
galaxy. As one of the examples, we compare our results at a viewing angle of
$25degr$ with the results of IC342. The relation between azimuthal angle and
Faraday depth of the numerical result shows a tendency similar to IC342, such
as the peak numbers of the Faraday depth.

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