Issue |
A&A
Volume 405, Number 2, July II 2003
|
|
---|---|---|
Page(s) | 513 - 524 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361:20030628 | |
Published online | 19 June 2003 |
Magnetic fields and ionized gas in the local group irregular galaxies IC 10 and NGC 6822
1
Astronomical Observatory, Jagiellonian University, ul. Orla 171, 30-244 Kraków, Poland
2
Astronomisches Institut der Ruhr-Universität Bochum, Universitätsstr. 150, 44780 Bochum, Germany
3
Radioastronomisches Institut der Universität Bonn, Germany
4
Max-Planck-Institut für Radioastronomie, Postfach 2024, 53010 Bonn, Germany
Corresponding author: K. Chyży, chris@oa.uj.edu.pl
Received:
28
February
2003
Accepted:
24
April
2003
We performed a high-sensitivity search for galaxy-scale
magnetic fields by radio polarimetry at 10.45 GHz and
4.85 GHz with the Effelsberg 100 m radio telescope,
accompanied by Hα imaging, for the two Local Group
irregular galaxies IC 10 and NGC 6822. Their star-forming bodies are
small and rotate slowly. IC 10 is known to have a very high
star-forming activity, resembling blue compact dwarfs, while
NGC 6822 has a low overall star-formation level. Despite
very different current star formation rates, our Hα
imaging revealed a large web of diffuse Hα filaments
and shells in both IC 10 and NGC 6822. Some of them extend
far away from the galaxy's main body. The total power
emission of both objects shows bright peaks either at the
positions of optically strong star-forming clumps (IC 10) or
individual regions or supernova remnants
(NGC 6822). However, in both cases we detect a smoothly
distributed, extended component. In IC 10 we found clear evidence
for the presence of a diffuse, mostly random magnetic field
of
14 μG strength, probably generated by a fluctuation dynamo.
One of the Hα-emitting filaments appears to be
associated with enhanced magnetic fields. We also rediscuss
the reddening of IC 10 and its implications for its distance.
In the case of NGC 6822 we found only very
weak evidence for nonthermal emission, except
perhaps for some regions associated with local gas
compression. We detect in both galaxies small spots of
polarized emission, indicative of regular fields (
3 μG),
at least
partly associated with local compressional phenomena.
Key words: polarization / galaxies: irregular / galaxies: magnetic fields, galaxies: individual: IC10, NGC 6822 / radio continuum: galaxies
© ESO, 2003
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