The Role of the Magnetic Field in the Interstellar Medium of the
  Post-Starburst Dwarf Irregular Galaxy NGC 1569
  (abridged) NGC 1569 is a nearby dwarf irregular galaxy which underwent an
intense burst of star formation 10 to 40 Myr ago. We present observations that
reach surface brightnesses two to eighty times fainter than previous radio
continuum observations and the first radio continuum polarization observations.
These observations allow us to probe the relationship of the magnetic field of
NGC 1569 to the rest of its interstellar medium. We confirm the presence of an
extended radio continuum halo at 20 cm and see for the first time the radio
continuum feature associated with the western Halpha arm at wavelengths shorter
than 20cm. The spectral index trends in this galaxy support the theory that
there is a convective wind at work in this galaxy. We derive a total magnetic
field strength of 38 microG in the central regions and 10-15 microG in the
halo. The magnetic field is largely random in the center of the galaxy; the
uniform field is ~3-9 microG and is strongest in the halo. We find that the
magnetic pressure is the same order of magnitude but, in general, a factor of a
few less than the other components of the interstellar medium in this galaxy.
The uniform magnetic field in NGC 1569 is closely associated with the Halpha
bubbles and filaments. We suggest that a supernova-driven dynamo may be
operating in this galaxy. The outflow of hot gas from NGC 1569 is clearly
shaping the magnetic field, but the magnetic field in turn may be aiding the
outflow by channeling gas out of the disk of the galaxy. Dwarf galaxies with
extended radio continuum halos like that of NGC 1569 may play an important role
in magnetizing the intergalactic medium.
