THE MAGNETIZED GALACTIC WIND AND SYNCHROTRON HALO OF THE STARBURST DWARF GALAXY IC 10

Abstract

ABSTRACT 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 IC 10, 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 IC 10 in total intensity, extending twice more than the infrared-emitting galactic disk. The halo is magnetized with a magnetic field strength of 7 μG in the outermost parts. Locally, the magnetic field reaches about 29 &mgr; G ?> in H ii complexes, becomes more ordered, and weakens to 22 &mgr; G ?> in the synchrotron superbubble and to 7–10 μG within H i 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 H ii complexes of about 60 km s−1, exceeding the escape velocity of 40 km s−1. Hence, the magnetized galactic wind in IC 10 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.