  We aim to explore whether strong magnetic fields can be effectively generated
in low-mass dwarf galaxies and, if so, whether such fields can be affected by
galactic outflows and spread out into the intergalactic medium (IGM). We
performed a radio continuum polarimetry study of IC10, the nearest starbursting
dwarf galaxy, using a combination of multifrequency interferometric (VLA) and
single-dish (Effelsberg) observations. VLA observations at 1.43 GHz reveal an
extensive and almost spherical radio halo of IC10 in total intensity, extending
twice more than the infrared-emitting galactic disk. The halo is magnetized
with a magnetic field strength of 7 microG in the outermost parts. Locally, the
magnetic field reaches about 29 microG in HII complexes, becomes more ordered,
and weakens to 22 microG in the synchrotron superbubble and to 7-10 microG
within HI holes. At the higher frequency of 4.86 GHz, we found a large-scale
magnetic field structure of X-shaped morphology, similar to that observed in
several edge-on spiral galaxies. The X-shaped magnetic structure can be caused
by the galactic wind, advecting magnetic fields injected into the interstellar
medium by stellar winds and supernova explosions. The radio continuum scale
heights at 1.43 GHz indicate the bulk speed of cosmic-ray electrons outflowing
from HII complexes of about 60 km/s, exceeding the escape velocity of 40 km/s.
Hence, the magnetized galactic wind in IC10 inflates the extensive radio halo
visible at 1.43 GHz and can seed the IGM with both random and ordered magnetic
fields. These are signatures of intense material feedback onto the IGM,
expected to be prevalent in the protogalaxies of the early Universe.
