J. Knapik

Jagiellonian University, Cracovia, Lesser Poland Voivodeship, Poland

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Publications (4)8.76 Total impact

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    ABSTRACT: 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 H Ii 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 mu G 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 mu G), at least partly associated with local compressional phenomena.
    Full-text · Article · Jul 2003 · Astronomy and Astrophysics
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    J. Knapik · K. Chyży · M. Soida · M. Urbanik · D. Bomans · U. Klein · R. Beck

    Full-text · Article · Jan 2001
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    J. Knapik · M. Soida · R. -J. Dettmar · R. Beck · M. Urbanik
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    ABSTRACT: According Co the classical axisymmetric dynamo concept, differentially rotating galaxies which lack organized optical spiral patterns and density wave flows should still have spiral magnetic fields with a substantial radial component. To check this hypothesis we observed two flocculent spirals, NGC 3521 and NGC 5055, in the radio continuum (total power and polarization) at 10.55 GHz with a resolution of 1.'13. A search for traces of optical spiral patterns has also been made by observing them in the Her line and by filtering their available blue images. NGC 3521 and NGC 5055 were found to possess a mean degree of magnetic field ordering similar to that in grand-design spirals. However, the polarized emission fills the central region of NGC 5055 while a minimum of polarized intensity was observed in the inner disk of NGC 3521. This can be explained by a more uniform star formation distribution in the centre of NGC 3521, while a higher concentration of star-forming activity in the nuclear region and in the rudimentary spiral "armlets" of NGC 5055 leaves broader interarm regions with unperturbed regular magnetic fields. Both galaxies possess regular spiral magnetic fields with a radial component amounting to 40% - 60% of the azimuthal field. The use of beam-smoothed polarization models demonstrates that this result cannot be produced by limited resolution and projection effects. Furthermore, a large magnetic pitch angle cannot be entirely due to the influence of rudimentary spiral-like features visible in our H alpha and enhanced optical images. Thus it appears that the dynamo process is responsible for the radial magnetic field in flocculent galaxies. The measured radial magnetic field component as compared to the azimuthal one is even stronger than predicted by a classical turbulent dynamo which provides arguments in support for modern, non-standard dynamo concepts.
    Preview · Article · Oct 2000 · Astronomy and Astrophysics
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    ABSTRACT: Traditional views considered usually the galactic magnetic field perfectly frozen into the gas while the interstellar turbulence can only randomize the field structure. In the last decade polarization studies of nearby spirals gave evidence that turbulent motions may generate regular magnetic fields, which itself are only partly tied to the gas. As a result of our recent observations we found clear evidence for dynamo action without contamination from spiral arm flows. We present also examples of magnetic fields probably decoupled from bulk gas motions. We definitely prove the existence of regular magnetic fields in an irregular galaxy, which supports non-standard dynamo theories, like the buoyancy dynamo.
    Preview · Article · Nov 1999

Publication Stats

46 Citations
8.76 Total Impact Points

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Institutions

  • 2003
    • Jagiellonian University
      Cracovia, Lesser Poland Voivodeship, Poland
  • 2000-2001
    • Ruhr-Universität Bochum
      Bochum, North Rhine-Westphalia, Germany