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  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 IntroductionIrregular galaxies are low-mass objects exhibiting a variety of rotational properties with a subclass of them rotating very slowly (rotational speeds V rot ≤ 30 km s −1 ) and often chaotically (e.g. Lo et al. 1993). They constitute important laboratories for large-scale interactions of stars with the interstellar medium: the low gravitational potential and relatively small size increase the probability that superbubbles, forming close to star-forming regions, may break out of the galaxy (e.g. Mac Low & Ferrara 1998). Many irregular galaxies exhibit giant arcs or filaments of ionized gas (e.g. Sabbadin & Bianchini 1979;Hunter et al. 1993;Bomans et al. 1997). The role of magnetic fields in the origin and confinement of these ionized structures (e.g. Hunter & Gallagher 1990) is still a matter of debate.In spiral galaxies magnetic fields, which are sufficiently strong to trigger star formation via magnetic instabilities (Blitz & Shu 1980) or to influence the superbubble expansion (Ferriere et al. 1991), are probably generated by the mean-field dynamo (see . This requires strong Coriolis Send offprint requests to: K. Chyży, e-mail: chris@oa.uj.edu.pl forces (hence a rapid rotation) to give the turbulent motions a preferred sense of twisting. A sufficient size of the ionized gas envelope is also required. Large irregulars...

We present a multiwavelength radio study of the nearby galaxy pair Arp 269 (NGC 4490/85). High sensitivity to extended structures gained by using the merged interferometric and single dish maps allowed us to reveal a previously undiscovered extension of the radio continuum emission. Its direction is significantly different from that of the neutral gas tail, suggesting that different physical processes might be involved in their creation. The population of radio-emitting electrons is generally young, signifying an ongoing, vigorous star formation -this claim is supported by strong magnetic fields (over 20 µG), similar to the ones found in much larger spiral galaxies. From the study of the spectral energy distribution we conclude that the electron population in the intergalactic bridge between member galaxies originates from the disk areas, and therefore its age (app. 3.7-16.9 Myrs, depending on the model used) reflects the timescale of the interaction. We have also discovered an angularly near Compact Steep Source -which is a member of a different galaxy pair -at a redshift of approximately 0.125.

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