J/A+A/585/A21 M83 magnetic and gaseous spiral arms images (Frick+, 2016)
Magnetic and gaseous spiral arms in M83.
Frick P., Stepanov R., Beck R., Sokoloff D., Shukurov A., Ehle M.,
Lundgren A.
<Astron. Astrophys., 585, A21-21 (2016)>
=2016A&A...585A..21F 2016A&A...585A..21F (SIMBAD/NED BibCode)
ADC_Keywords: Galaxies, nearby ; Magnetic fields ; Radio sources
Keywords: magnetic fields - magnetohydrodynamics (MHD) - galaxies: ISM -
galaxies: individual: M83 - galaxies: spiral -
galaxies: magnetic fields
Abstract:
The magnetic field configurations in several nearby spiral galaxies
contain magnetic arms that are sometimes located between the material
arms. The nearby barred galaxy M83 provides an outstanding example of
a spiral pattern seen in tracers of gas and magnetic field. We analyse
the spatial distribution of magnetic fields in M83 and their relation
to the material spiral arms. Isotropic and anisotropic wavelet
transforms are used to decompose the images of M83 in various tracers
to quantify structures in a range of scales from 0.2 to 10kpc. We used
radio polarization observations at λ6.2cm and λ13cm
obtained with the VLA, Effelsberg and ATCA telescopes and APEX sub-mm
observations at 870µm, which are first published here, together
with maps of the emission of warm dust, ionized gas, molecular gas,
and atomic gas. The spatial power spectra are similar for the tracers
of dust, gas, and total magnetic field, while the spectra of the
ordered magnetic field are significantly different. As a consequence,
the wavelet cross-correlation between all material tracers and total
magnetic field is high, while the structures of the ordered magnetic
field are poorly correlated with those of other tracers. The magnetic
field configuration in M83 contains pronounced magnetic arms. Some of
them are displaced from the corresponding material arms, while others
overlap with the material arms. The pitch angles of the magnetic and
material spiral structures are generally similar. The magnetic field
vectors at λ6.2cm are aligned with the outer material arms,
while significant deviations occur in the inner arms and, in
particular, in the bar region, possibly due to non-axisymmetric gas
flows. Outside the bar region, the typical pitch angles of the
material and magnetic spiral arms are very close to each other at
about 10°. The typical pitch angle of the magnetic field vectors
is about 20° larger than that of the material spiral arms. One of
the main magnetic arms in M83 is displaced from the gaseous arms
similarly to the galaxy NGC6946, while the other main arm overlaps a
gaseous arm, similar to what is observed in M51. We propose that a
regular spiral magnetic field generated by a mean-field dynamo is
compressed in material arms and partly aligned with them. The
interaction of galactic dynamo action with a transient spiral pattern
is a promising mechanism for producing such complicated spiral
patterns as in M83.
Description:
We performed radio continuum observations of M83 with the Australia
Telescope Compact Array (ATCA), consisting of six parabolic dishes,
each of 22m in diameter, forming an east-west radio interferometer.
We observed M83 with different baseline configurations, each
observation session lasting 12h to achieve maximum uv coverage.
Objects:
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RA (2000) DE Designation(s)
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13 37 00.92 -29 51 56.7 M83 = NGC 5236
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
list.dat 143 14 List of fits images
fits/* . 14 Individual fits images
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Byte-by-byte Description of file: list.dat
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Bytes Format Units Label Explanations
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1- 9 F9.5 deg RAdeg Right Ascension of center (J2000)
10- 18 F9.5 deg DEdeg Declination of center (J2000)
20- 22 I3 --- Nx Number of pixels along X-axis
24- 26 I3 --- Ny Number of pixels along Y-axis
28- 37 A10 "date" Obs.Date Observation date
39- 48 E10.5 Hz Freq ? Observed frequency
50- 53 I4 Kibyte size Size of FITS file
55- 85 A31 --- FileName Name of FITS file, in subdirectory fits
87-143 A57 --- Title Title of the FITS file
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Acknowledgements:
Rainer Beck, rbeck(at)mpifr-bonn.mpg.de
(End) Patricia Vannier [CDS] 17-Feb-2016